Many variables.
Which ramp, for roosts, for nests, for coop?
A lower angle, 30-35 degrees, is what I've found to be best.
You can prop the lower end on a concrete block(16") to reduce angle and ramp length.
Height of nests and roosts can depend on coop width/length too....so you don't have flyers crashing into things.
Roost are best always higher than nests, so they don't sleep(and poop) in nests.
Here's my theory on the 'stack up' aspect to coop design:
Bottom of pop door are best about 8" above floor so bedding doesn't get dragged out of coop.
Nice to have bottom of nests about 18" above bedding to allow use of that floor space under them(doesn't count if your nests are mounted on outside of coop).
Roosts are best about 12" higher than nests so birds won't roost(sleep) in nests and poop in them, if you use poop boards under roosts it will also 'stretch' your floor space.
Upper venting is best as high as possible above roosts so no strong drafts hit roosts in winter...and hot/moist air and ammonia can rise and exit coop.