That is the wrong question. The real question is: Why would you consider DIY? The answer for an investor / entrepreneur is: You wouldn't, ever!
Follow up questions:
- Are you a GC?
- Do you have knowledge & experience managing crews of various trades?
- Do you the appropriate insurance & licenses/permits as a GC?
- What is the opportunity cost for your time?
As an investor / entrepreneur, you're running a business. An apartment complex is a business. Taking time out of your day to DIY technical trades oftentimes will cost you more in the end. If you have little to no experience as a GC, the project will likely take longer (increased holding costs), be a lower quality (decreased value), and keep you away from running your business (lost opportunity). Businesses that are operated that way are small and stay small. Those business owners really just own their own job.
Unless you have good experience as a GC and don't mind staying small, the only real reason to consider DIY is if you overpaid for it and want to save on labor costs. But again, don't even do that if you don't know what you're doing.