I had saved close to 30% or about $100K by GC ing our own "gut out" rehab, on our personal residence. BUT it was not easy, and i had probably cost us about $5k-$8K in mistakes. Read On!!!
I had some smaller rental rehab experience, kitchens, BAs small addition(legal ones). In order to completely rehab our personal residence I had to became a full time contractor for close to 20 months (felt like 60 months) Luckily there was a slow down time in RE investing (when folks line up to buy every listed house) so I had time available to me to do this.
And in order to be able to successfully finish the project I had to learn:
To make my own copper roofing
The professionals quoted me about $30K to cover with copper a small roof (no more than1.5-2 squares) on front porch, so I learned online how do do coper roofing borrowed and metal bender from a friend and purchased copper for $2500 wholesale.
I had to learn to do pluming so I could shows my helpers what to do, and a master pulled a permit for me and checked all of our work.
Same for electric.
Most work past on first some on second try.
I had to learn how to build oak stairs, with iron railing. (toke me a week and a half with one helper) it looks like a pro job but a real pro would have done it in two days.
I had to also learn how to set up a computer network for entire house with LAN cables for every room so i can plug in a computer everywhere laundry room, garage included, with connecting to a network hub in closet.
For HVAC we had relationship from our rentals, so we had pros doing it including sizing it professionally for new widows/insulation, and a completely independent system for each floor. (no too hot/too cold floors)
Drain tiles, I had no experience but I had watched a lot of Holmes on Homes (our county inspector is also fan of that show) So it was done correctly by my helpers per my instructions and ok'd by county.
In one day I had drive to 12 different Homedepots to try to match the Marble stock that was running low for our Master BA....as you pros are well aware you can not do marble floor in two steps (especially white ones) it is almost a must to finish an entire surface the same day..... what a pain in the a##.. that was!!
Doors and windows, insulation ......etc....
Looking back now, It felt like my head was going to explode by having to learn all different trades all at once while almost all the deadlines were broke. ( My wife called my the "two weeks contractor" because i told her so often for months, that we will be done In two weeks. :)
I learned a lot and it comes very handy now when I hire contractors for our rentals, BUT I am not sure if I would do it again knowing what I know now. May be I should have just waited a few years and give it to a trustworthy professional with lots of experience!