So we are building with an architect for service phases 1-9. Our structural engineer took care of the statics and energy saving ordinance. The architect, together with the structural engineer, created the execution plans. If you know craftsmen, you can still award the contracts through the architect, unless you want to award them off the books. Our neighbor did exactly what you are planning and now he has to deal with every mess from the trades, which he actually already knew well. He is on the construction site every day, has to check, inspect, and coordinate everything alone, you must not underestimate that, and so many things went wrong for him, like the cistern installed without a proper slope angle, so now the water doesn’t flow into the cistern at all. I wouldn’t recommend it to you without construction supervision. As mentioned above, we are building with our architect and so far we have zero stress, we are on the construction site about once a week and it’s going well. For that, the architect is on site daily and sends us pictures. Definitely “book” up to service phase 9 because of the extended warranty.