Joseph,
There are some great contractors, but most can be flaky. Unless you have had prior experience with the contractor and trust them, always buy the materials yourself. You can mitigate your potential losses with a general contractor greatly if you do labor only. I have flipped 16 houses in the last 3 years and I highly recommend this model.
For example, kitchen remodel is lets say $25k. Materials 10K and Labor is 15k.
Contractor buying materials - Contractor asks for half upfront and potentially walks away with $12.5k
You buying materials (Labor only) - you pay half upfront of $7.5k and contractor quits on you, you lose out on $7.5k
When you purchase the materials and the contractor walks away with it, it now becomes a criminal issue and not just a civil case, because you paid and own the materials. This might sound extreme, but many new investors get burned by contractors.
Make a Home Depot Pro Xtra account and have the contractor checkout using your phone number. In real time, when the contractor is at the register, you get a live link to the receipt of the items they are purchasing, you can either confirm or deny.
Best of Luck,
Kristina Kuba
Keller Williams Tampa Central