"I called him in April and he said it would be May, due to some delays in setting up his shop"

If he is involved in some big move etc... that can be a huge time issue, you might want to look into that first.

There are lots of reasons to be slow, but builders who can't deliver on dates reliably should not take deposits. I know some craftsmen who won't do it because they end up spending all their time with people who want their stuff. Bettert to have the flow under control, but if you can't don't take money up front. Or call for a deposit when the frame is being started.

I know a few big names who don't do their own welding.