Deciding to lift a 100-year-old house in Seattle, reframe the lower level, pour a new slab, redo all the electrical in the house, and do all new plumbing without hiring any contractors...while my wife was on maternity leave for our second child.

Project took a lot longer than we expected, cost more than I budgeted, and made life very unpleasant (we were entering the house through a ladder for a few months...), but when we were done we had a 2 br 1 bath with kitchen apartment we could rent out.