I've never built a wheelchair ramp so I don't know the codes but what I can suggest is not to start building until after you have drawn a "stair Plan". All your decisions are made in plan view. You need to know your total rise, desired pitch, either the inside or outside radius and ramp width. From there it is a matter of finding the circumference of those radius then the portion of the circle you need.
For example:
30" rise
15' inside radius
desired pitch 4.76 (where is this measured- inside radius, walk line or center or ramp)
Lets pick the inside radius the point where the pitch is measured, that will make to others lower.
Lets say a 48" ramp width which will make the outside radius 19'
30" rise and 4.76 pitch= 360 1/4" run in plan view
total circumference of a circle with a 15' radius (inside stringer) (2Pixr) is 1131"
360.25/1131=.318523
.318523x360°=114.7°
114.7° is the run of the ramp without landings, etc.
outside stringer circumference 19' 2π19'= 1432 9/16"
divide 1432 9/16" by 360°=4" per degree, multiply by 114.7°= 456 7/16"
456 7/16" run, 30" rise= 3.76° pitch of outside stringer.
The middle of the ramp pitch would be?
attached is a typical single point radius stair plan.