I've made two ampmaker kits, the WF55 mentioned above, and the P18, and 18 watter now discontinued. I've got it's successor, the P1800 in a box waiting for some time to get started on it. The instructions provided are very good. Prior to making my first I'd made a few pedals and done some pedal mods, always following instructions.
Both amps I've made will last a lifetime I'm sure, they're both very decent quality. There are certainly a few nervous moments when you do the first tests, but following the instructions carefully gave me confidence. However next time I might get a friend who is a more experienced builder to give it the once over before I do the live tests.