Hi theOrange77 and welcome to the forums!
Your idea of being able to use multiple builders for one project is great, and would certainly make upgrading easier for players. Unfortunately, however, it's been ruled out by Supercell, probably because players would use multiple builders instead of buying gems, which would cut profits.
Please be sure to read the rest of the ruled out ideas located in the sticky
HERE.
Thank you for taking the time and effort to be a part of this wonderful community and posting your ideas for how to make the game better. Clash On!