Permits. You have to have one to start the project, get the county and utilities to agree to it with proper plans, THEN you have to install according to plans including following all fire codes and electrical standards for your county, state, and federal. After that you have to get it inspected and approved by that utility and county. I’ve been doing these projects for 5 years now. Most of the DIY stuff is almost always against code and ready to be shut down at any minute if anything else happens and requires a city inspector at the home. Not to mention that if you do anything to cause problems with your roof, electrical, or water because of your DIY you don’t have any warranty to cover it. Sorry but all these small cost explanations are avoiding the reality just focusing on price. Good luck especially if you actually know what you are doing versus majority of people on this thread. Not everyone builds their own cars even though they can technically do it all themselves. There’s a reason why that is.