I mean, it's possible, but...
1. (7%) Are you really going to buy something without a real estate agent?
2. (20%) Are you really going to save this? Or end up spending twice as much time as a GC would because you're trying to figure things out? I've never seen a builder markup over 15% anyway.
3. (4%) Material savings? You, the general consumer will not get any savings here. If anything the builders have developed relationships that provide bulk discounts. You'll probably pay retail for most materials unless you have a source.
4. (2%) Cost saving construction? What does that even mean? When you're not a GC who knows what they are doing I wouldn't put it past the subs to "convince you" that you need something you probably don't.
5. (9%) Doing the work yourself. Ok. You probably could do that one if you know how to paint / drywall / install cabinets / tile / lay floors, etc. etc.
My guess is that while this is all very appealing, you may save 9% or more but it may take you twice, or three times as long to finish.
What happens when a construction conflict arises and because you're not sure how to solve it, all your subs pull off the job until you figure it out. When you're ready to start again they say "Ok. But we have to finish this job now. We can be back in 6 weeks."
Find a good GC. They will be your best friend. Not sure how? Call some architects and ask who the good ones are.
Good luck!