You must understand that reports are not for reading on the screen. They are meant for printing on paper. Therefore, you would never have scroll bar on a report, and in Access you cannot add one for this reason. The scroll bar would be located on the datasheet view of a subform in a FORM, not a report.
Since a report is to be printed, you must design your report to match the paper size available to your printer. Therefore, if your printer can only do 8½x11 (letter) paper, your report should be no longer than that. If your printer can handle 8½x14 (legal) or even 11x17, then you can design a report for those.
For those cases, your margins, fonts, font sizes, page orientation (portrait vs. landscape), and number of fields per row will determine how you design the report; but you're always limited by the paper size.
Michigan Dept. of Environmental Quality, Air Quality Division