Just to check back in - I had a really good time.
I wasn't sure what to do, but I volunteered with roofing and turned out to be pretty good at it! I also tried siding but was pretty crap at that (I couldn't hammer hard enough to get the nail in without losing precision and smashing my thumb... which I wasn't willing to do), but it was ok since I did roofing for most of the day and apparently we got it done a lot faster than usual.
My first ~10 minutes on the roof were kind of "oh ****" since I'd never even even been on the roof and it was pretty pitched. I was convinced I was going to fall over at first. But I got used to it faster than I thought and was pretty comfortable up there after awhile.
Also surprised myself by being more "in shape" than I expected (I don't workout). Some people had trouble squatting along the roof, or hammering, but I was able to keep the squatting up throughout the day without significant trouble. My legs ARE killing me today, and they were so tired they vibrated/shook when I came down the ladder (I think the guy holding the ladder thought I was terrified of heights because he kept trying to talk me down
"It's ok, almost there, there you go").
Anyway had a good time and feeling good about myself too.
Edited to add - one thing I learned about them too is, the houses they 'give away" aren't free. They give them to families who do meet certain income requirements (above a certain threshhold but below another threshhold) who wouldn't be able to afford a standard house/mortgage and have some sort of need (usually a family). The main thing the families get are a 0% mortgage that has low labor fees, but they do actually pay for the house. They also have to help build their own house and 5 other people's houses, for 8 weekends per house, and go to classes for the first year on topics like financial management, caring for a home, being a good neighbor, etc. So it's not really just a 'free house', and it was pretty cool to get to meet a lot of the families there helping out.