I used to work with a non-profit that did home repairs for folks who could not afford to pay for them. We did everything but roofs and plumbing. I did it for 7 years...about 6-7 projects/year. Maybe 1/3 of those were either permanent handicap ramps, or had ramps as a component of the project. There were some county government resources (we worked in 2 counties), but this is a rural area so resources were scarce. I directed some folks to a state program, but I'm not sure what those programs covered.
Habitat For Humanity started doing repairs as well as new home construction (their Brush With Kindness program), but like their homes, the recipient has to pay. Labor is free unless the work has to be contracted out (HVAC plumbing, etc.) The cost of materials (and contracted labor) gets passed through with no markup. If the materials or contracted labor are donated, there's no cost for that part of the project to the recipient. Habitat sets up loans for the recipient at a very low rate, and the payments go back into the kitty to fund other projects/loans. They wanted to partner with us at the local level since they needed people with our skills, but we never charged for what we did, and we did not want to partner on projects where the recipient was left with a payment.
If anyone is looking for this kind of help, just call any of the local non-profits that do this sort of work. Any one of them can point you to whatever resource might be the best fit, since they all work together and generally know what's out there. There are probably income requirements. Each affiliate for the national outfit I was with had their own maximum household income that qualified, set as a % of that county's average income.