i've got to build one for a friend. can anyone tell me what code is for rise/run.

Call the building inspector in that particular town Paul! They all like to make up their own code as they go along! Best to check the local jurisdiction on that!

http://www.mobility-advisor.com/wheelchair-ramp-specs.html
Here is a place to start. Keep in mind that ADA specs are the minimum that you need to be compliant with ADA and are a generic spec designed to meet most of the needs of most handicap people. If it is for a individual with limited mobility it would be better to tailor the ramp to meet their needs.

1' to an inch of rise. Any run over 20' needs a rest area. I think these #s are still good. Safest bet is call the building inspector where the ramp is going.

I built one in Nevada about 15 years ago for a friend and had to use 1 1/2" due to limitations areawise and it was brutal.

Current code is a maximum of 1:20, with a maximum rise of 30 inches, with a rest area or landing at least 60 in long at the end of the run. See section 4.8 for other details (handrails, etc)

http://www.ada.gov/adastd94.pdf