Plus Cover means that the cover of the booklet is printed on a different paper, usually of a heavier weight, than the rest of the pages. This provides a bit more structure to the book and can help keep the books upright if they are in a rack or just give a nicer feel in hand. Also, with cover weight paper, additional finishing options like lamination and spot coating become available. It is called "Plus Cover" due to how it is described when providing specifications or getting quotes. The number of inside pages is the variable factor because a cover portion is always one sheet (4 pages), so a page count would be described as, for example, "24 pages plus cover" for a total page count of 28 pages. When the cover is printed on a different paper, it is indicated as "Plus Cover" so the printer knows right away there are two different stocks required.

It is the most cost-effect bindery method for booklets, for short runs as well as high volume runs. As the process is almost entirely done inline on one machine, it is quicker than other styles of binding. Having the cover on a different stock opens up the option to add additional finishing like lamination or spot coating. 3-hole punching at the spine can be added to allow the book to be inserted into a standard 3-ring binder It allows for artwork or images that span two adjacent pages (crossover images) Plus Cover books are still ideal for mailing projects. However, the total mass of the piece will need to be taken into account when designing, as the added weight of the cover can reduce the number of inside pages possible while still remaining within the grammage allowances for the different postal rates.

Saddle-Stitching requires the page count to be in multiples of four because there are 4 book pages printed on each sheet. There need to be at least two sheets (8 pages) for the inside of the book so that the minimum number would be 8 inside pages plus 4 covers pages, for a total of 12.

For books with the inside pages printed on a lighter weight stock, in the 50-70lb range, the maximum page count would be 60 pages, plus the cover. If a thicker paper is desired for the inside pages, such as 80 or 100lb, it is recommended to keep the page count below 36 inside pages, plus the cover. The weight of the cover stock can also have an effect on the maximum page count, as a thick, heavy cover will reduce the number of inside pages that the stitching machine can accommodate. This is because the sheets are gathered on top of each other, stapled on the spine, and folded. If the spine is too thick, it will not fold nicely and can "bubble" open rather than laying flat.

Even though the cover portion is done on thicker stock, there is still no room on the spine for printing.

Yes, you can. But only as a custom quote.

Files can be supplied as one PDF containing the inside pages and one that contains the cover, or as a single file with all of the pages in it. Either way, the file(s) should be exported directly from the design software as "Single Pages" instead of multi-page spreads (for example, a 5.5x8.5 book should be exported as 5.5x8.5 pages and not as 11x17 spreads that each has 2 pages) A minimum of .25" or 1/4" of safe margin is required for all booklets. This means that page numbers, images, text, and any important elements that are not intended to go right to the edge should be at least .25" away from the edges. There can be natural variation in the cutting process, as the operator cannot guarantee that every booklet will be cut in exactly the same place. Secondly, a circumstance known as "Creep" can occur with saddle stitching, especially with thicker paper stocks. Creep is where the bulk of the paper at the spine due to the gathering of the sheets causes the inner pages to extend or "creep" further out than the cover when folded. Below is an exaggerated view of how the inner pages extend beyond the edge of the outer pages when folded (this is for illustrative purposes only. The actual amount of creep is usually between 0"-.125", depending on paper weight and page count).

If you want the same thickness for the cover and the inside pages, your product should be Saddle Stitch Bound Books (Self Cover).

In that case, you can only upload the file for the cover. When you select your product options and get to the file upload section, you can turn off the 'Multiple files' button. This will allow you to upload only one file without getting the error message. To let us know the inside pages are blank, you can leave a comment.

The hard copy proof can be ordered by selecting it from the Proof Group dropdown list.

We could do 80 pages + covers, but that would be the machine's maximum, and there can be issues with how it folds. If you insist on 80 pages, it would be better to change the binding type to perfect bound or coil bound.

The size refers to a single page size, so that is the size of a closed book.

Margins and Columns are important tools for creating the structure of a document, whether it is a multipage document or a poster. The first that should be defined are the margins. Before this is done, it is important to understand their function. Visually, margins cage the content and support the structure of a layout. They provide a resting place for the reader's eyes as well as supporting the tone of the design. There are also some common practical functions to consider:  How much room is needed for holding the content?  How is the item going to be used? Will it be bound?  Are there other considerations that need to be taken into account? One example would be a street poster/advertisement where the print is held in a large frame, requiring oversized margins. Has enough "Safe" margin bee allowed? This is the distance between the edge of the piece and any elements to ensure nothing is cut off.When defining margins for facing-pages, the two pages should be treat as one document and appear together. This layout will typically be used for newsletters, reports, magazines etc. Margins are usually set in the following order: inside (smallest), top, outside and bottom (largest).  Start by going to File > New > Document. Within the floating palette three quarters of the way down is the margin section  
Changing Margins 
Once the margins are set using the new document palette, it is possible to redefine them. Make sure to select the pages to be edited. Check this by opening the Pages palette, if it is not open go to Window > Pages. 

Once the palette is open hold down Shift and click the pages to be edited and go to layout > Margins and columns. Within this option box the measurements can be edited. By using this method it is possible to have different margin setups on each individual page, just select one or a number of pages still holding down shift and go into the Margins and Columns palette. The pages which were not selected will remain the same.  How to Make Columns in InDesign
1. First, load an existing InDesign project or select "File" > "New" to start a new one. In the New Document window, choose the Number of Pages and Page Size, and then find the Columns section. 

Here, the number of columns to add on each page can be defined, and how much blank space to have between columns (the Gutter setting). InDesign will automatically adjust the columns so that the gutter width is maintained throughout the project.        

2. If the document is an existing project, it only takes a few steps to add new columns. First, find the Pages menu and double-click on the page that need to be edited. Click on the page that the columns are to be added to, and then choose "Layout" > "Margins and Columns" (or press Ctrl/Command+B). In the Columns section, the desired number of columns and gutter width can be added.   

3. Finally, any overset text in the project can be placed in a new column. To do this, draw a text frame next to an existing column, choose the Selection tool, and click on the overset text icon (it looks like a red + symbol). Move the cursor over the new text frame until it changes shape, and then click once. Now, the overset text will continue into this new column.  

How to Add Columns to a Text Frame
To create columns in an existing text frame, choose the Selection tool and click on a frame to select it. Then, go to "Object" > "Text Frame Options". Just like the Margins and Columns window, this dialog box allows the number of columns, the gutter width, and column width to be defines. If "Fixed Column Width" is selected, the column width will stay the same when the text frame is resized. Finally, if "Balanced Columns" is enabled, the text will be dispersed between columns so that each text block is the same length. 
 
How to Add Columns to Master/Spread Pages
To add columns to multiple pages across an InDesign project, first find the Pages menu and click on a master page. If only one spread is to be targeted, just click on the page numbers that comprise the entire spread. Next, choose "Layout" > "Margins and Columns", and adjust the columns and gutter width for that spread.