Along with Shar I've built a few trails and maintain more. If someone wants to help that's great. But a lot of the work I do is spur of the moment so not much warning. Some of the work is mid ride as tools are cached close by (note to other builders in Seymour - hide your stuff well - I had a pack and buckets/sieve pinched).
A lot of times I just pound away at trailwork as a change from a deskjob. It's cool to build something tangible or maintain an already nice line as opposed to making paper. While it's nice if people help I don't give much advance warning because I don't know myself. Long story short - just go donate to a local trail org. Or what Jerry said. Because Jerry is right