Everybody has the right and privilege to work on their own projects. In fact the Do-it-Yourself industry is growing. Whether or not a person does their own work or hires it done, the job must still abide by the laws governing inspections.
I have noticed that there is a great deal of difference in workmanship, usually depending on the experience factor of the person who performs the work. There have been a few cases I have seen where a “Do-it-Yourselfer” has been so particular in his or her work that the job was as good as a contractor. But that result is not common.
On the other hand I have seen workman in a particular trade do work so bad it could have been done by “Joe’s Pretty Good Garage Mechanics and Tradesman Coalition.” Through the years I have looked at the finished product of Electricians, Plumbers, and Carpenters. After awhile I could identify the company and the tradesperson involved by looking at the work.
Usually the difference was most notable between professional and non-professional.
On one job I watched a number of teen-aged boys on a scaffold trying to put up a sheet of 4’x8’ sheet rock. (The process for fastening sheet rock has changed over the years and I won’t comment on what is the more correct way to do it here.) These boys were using the process of placing the sheet rock in position, nail the corners, and then decide it was in the wrong location and remove the sheet.
When you remove a nailed piece of sheet rock, the nail heads pull through the sheet. This leaves a small nail-head size hole on the front side and a large divot of missing sheet rock on the back side.
The crew of teen-agers did this so many times that the sheet they were using became as limp as a dishrag. I guess they left it up to the taping and mudding to cover up. When it comes to taping and mudding, you can really tell the difference between professional and non-professional. A professional taper can tell the difference between a professional rock hanger and a Do-it-Yourselfer. (Just as much as a painter can tell the difference between professional and non-professional taper.)
One time we were on a job where the sheet rock dust was about ¼ inch deep on everything. It turns out that the rock hangers had been using a table saw to cut the rock to fit. Their clothes looked like they had been grinding grain into flour. It is usually not best to fit the rock so close that there is absolutely no space between pieces. (Then again, I’m not a sheet rocker or a taper and I don’t play them on T.V.)
Speaking of which, when my wife and I were building our home we used a lot of pieces of sheet rock left over from jobs we had been on. We wound up doing a lot of extra fitting and finishing. We also used some 4’x12’ sheets, which were hard to handle for two (inexperienced) people.
Years later I found that there is a tool for sheet rock hanging. They have a ceiling jack for the purpose of putting up large pieces of sheet rock and it works like a charm.
Which is why, generally speaking, no matter how much you know or want to do your own work, people with the right tools and experience will generally cost less than a D-I-Y project.