One of the biggest mistakes many real estate investors make is performing all of the renovation work on a fixer upper themselves; mistakenly believing it will save them money in the end. This line of thinking, however; can result in a number of problems; most of which will actually cost you money rather than save you money. Unless you are a professional renovator, and an expert in every area of renovation; chances are the work you perform isn't going to be up to code. That's no slight intended toward anyone, but there is a reason that most individuals employed in the construction trade specialize in one or two areas.
There's simply too much to know to be able to become skilled at every task with enough mastery to perform it at a level that will meet inspection regulations. If your renovations aren't up to par, you'll end up either unable to sell the property, having to sell it a price less than you intended or having to hire an expert to come in and do the work again. All three of these scenarios end up costing you money and detracting from you profit margin.
The second reason you shouldn't perform all of the work yourself is because your time is worth money. It just simply doesn't make any sense to spend the time that you could be utilizing toward other efforts just to save a few bucks. If you are employed with another job and real estate investment is just a sideline for you, then you will need to either take off time from your job or do the work on your own time.
Taking time off from work doesn't get you any farther ahead financially because even if you have personal time or vacation time, it's still costing you money to use those days because you're depleting a limited supply. Performing the renovation work on your off time detracts from your ability to spend leisure time with your family, relax and pursue pleasurable activities. This scenario generally results in problems with your family and you overwhelmed by exhaustion and stress.