I work as both a contractor with investors and as an investor.
I could never deal with an investor purchasing the materials.
Here are some reasons why:
An average rehab of 30k takes us about 2.5 weeks to complete with us buying the materials.
The same 30k rehab would take double that time with an investor who isn't available daily when we need additional paint or maybe anothr box of tile, or wait, what if the faucet he bought won't fit the undermount sink or what if the extra gallon of paint didn't match, etc, etc.... I would NEVER work with an investor who insists upon purchasing his own materials.
Next, I never buy anything at home depot or Lowes... I get materials 50% cheaper than what the HD or Lowes cost is. I do add 15% on to my price but the investor is still saving $ by allowing us to get materials.
I don't want anyone to know my sources for materials because it is how I always win the bid... If I told every investor where to get the materials then why would they need me? They could just hire cheap labor and totally cut me out.
Sure, they would probably suck at it and not do nearly as good of a job at managing the rehab as I do but money makes people do stupid things.....
We charge our investors 50% down, signing a waiver of ML, and 25% at the half mark of completion and the remainder at completion. It works well for us and we have their property back on the market in less than 3 weeks...
Most of my investors trust me completely to design the rehab, as well since I have always went with the thought that if I treat them right and do an outstanding job at a fair price, I will have repeat business and volume is what counts in construction. Plus, I know what sells... 75% of my projects go under contract within 30 days, the other 25% within 70 days, I have never had any go for more than 90. Numbers don't lie and if it ain't broke then don't fix it.
To each their own...
As an investor, I pay my company to rehab my projects and go along the same method of payment and cost as I would with any investor. Of course, it is in my best interest to do so for taxes but even if it were not, I would still do it that way because it's the right way.