It all starts here. Meeting with the agency referring the person needing the ramp and the client or caregiver will help you define the project. Good measurements are crucial and pictures help a lot. Remember 1" rise needs 1 ' of ramp so 20 inches will need a 20 foot straight ramp. Landings don't count in the run distance.
Draw it out. A visual plan helps everyone know what is going on and helps the planner insure that nothing is missed.
Define materials needed. Without a materials list something will usually be forgotten which means trips to get stuff and delays in the project.
Consider Safety, Security & Documentation. IF THE WORK SITE IS NOT SAFE AND SECURE NO NOT DO THE RAMP. Good documentation builds community support and is useful in fund raising.
Tearout can be time consuming.
How is the project going to effect the family?