In the "hire someone" vein, setting an artificial deadline can sometimes help. "If I don't build the X by Y myself, then we just go buy it."

As with anything, momentum builds too. If it's not something that has a lot of constraints, just looking for one little step is easier to accept than Starting The Project. Like, I'm not necessarily going to frame the new opening today, just cut a hole in the wall in the back of the closet. May depend on housemates' tolerance. But often just getting into the workshop is enough to overcome activation energy for me.