Helping timber frame GC build your house

What is the best way to approach finding a GC willing to let you help build your house? I’m currently retired, but not old. In good shape and very handy. Would like to help build my own house but don’t want the responsibility of GCing it myself. Would most GCs let you throw in with their crew each day to help out? Would they be against it for any reason? I see it as free labor for them, so why not?