I haven't seen a rule about this in a long time.
But, a long time ago, you could have as many spells as you wanted on a scroll. This didn't do anything but harm you as far as game mechanics.
You couldn't cast more than one at a time. You couldn't rip the scroll and hand off a spell to someone else. You still had to pay all the same amounts for each spell individually. Damage one and you damage all.
The only benefit I could see is only having to draw out one scroll, but then again, you could rule it takes time to find the spell you want as well.
I don't know anything about tattoo rules but I imagine that above would still apply.
|Tiny Coffee Golem|
Physical Description: A scroll is a heavy sheet of fine vellum or high-quality paper. An area about 8-1/2 inches wide and 11 inches long is sufficient to hold one spell. The sheet is reinforced at the top and bottom with strips of leather slightly longer than the sheet is wide. A scroll holding more than one spell has the same width (about 8-1/2 inches) but is an extra foot or so long for each additional spell. Scrolls that hold three or more spells are usually fitted with reinforcing rods at each end rather than simple strips of leather. A scroll has AC 9, 1 hit point, hardness 0, and a break DC of 8 (LINK).
Scroll Case: A leather or wooden scroll case easily holds four scrolls; you can cram more inside but retrieving any of them becomes a full-round action rather than a move action. You must destroy the scroll case to damage its contents (hardness 2 for leather or 5 for wood, 2 hit points, Break DC 15). A scroll case is not water-tight (LINK).
The rules do not say the maximum number of spells that can be crammed into a scroll, but I would think that 6 would be a reasonable maximum.
Given all that, a scroll can be as any length as long as you aren't taking storage into account. Since a scroll takes up the same space regardless of the spell level, most scrolls probably only hold one spell; occasionally, one may find a scroll with 2, 3, or 4 spells; and on rare occasions, scrolls with 5 or 6 could be found.