From what I can tell you have already got an Architect working for you to redesign your house? Can they find builders or are these the useless ones!!
Sorry, I can’t answer your original question but are going to pick up on something else instead – licenses.
Unfortunately, a lot more is classed as “major works” than in the UK..you need a minor works license for everything that does not alter the structure of the house or change its use..this starts with painting the inside… minor licenses are pretty easy to get, you simply fill in the correct form and hand over your money at the ayuntamiento! The license also means that you are covered if your builder has an accident whilst on site etc..builders are not meant to start work until you have the license…but having said that, it depends on the area, the builder etc as to what happens in reality!