Hi
im in the same boat as you. We sadly got refused our planning at the first hurdle as our neighbour objected. Our plan is to get a construction company to do the building work. We will use an electrician and a plumber separately. I can’t even bear the thought of the cost, but I think a construction company will charge more from start to finish. I have done this before, and the key is you must must shop around, even though it’s time consuming. We are on a very tight budget too.
Good luck