ALWAYS PURCHASE YOUR MATERIALS YOURSELF or else!
Anyone, and I really mean anyone that is doing any form of construction/rehab, a word of warning: Always buy whatever materials (lumber, cabinets, flooring, sheetrock, plumbing, tile, sprinkler system, lighting, etc., etc) you need for a project seperately with your own credit card/checkbook. You own it. Not the contractor. In all due respect to contractors/subs, never ever let a contractor or anyone else purchase materials other than yourself, esp. if you don't know them well. You can go with the contractor, but the actual register purchase should be with your own credit card/checkbook as the rightful owner.
Reason: If you ever have a falling out or dispute with anyone working on your project who purchased project materials, that they could easily claim it as theirs, take off site (steal??) or whatever, and still they bill you for it even if they never finish the project or left the materials on site, good luck trying to get it back in a dispute or if they walk off the job. Let's say you get into a dispute, you fail to pay them or withhold payment or the contractor/sub fails to show up again or whatever, and you have paid them some monies already, well, technically, until you pay for all materials, under most state laws, those materials are not yours.
If you personally purchased the materials seperately from the contractor/sub, that is your property irrespective of any disputes/claims the parties may have. You want to purchase and own the materials yourself, even if you have to go with the contractor/sub to do so, and it may be a pain, but having rightful ownership will at least mitigate any future disputes that may arise.
On the same note in CA, and likely in most states, any contractor can put a Mechanics Lien on your property's title pretty much at will. Simply filling out a form, and for $15, can go into the County Recorder's Office and record a ML against the title of your property without notice to you (you won't know until you do a title search and see the lien). He/she doesn't need lawyer either in CA. Getting it removed is a whole legal process. Though recording one on title without just cause is fraud, but a lot of good that does you while fixing/flipping your house up quickly.
ALWAYS get a clear Legal ML Waiver and release stating essentially the contractor has been paid and full, and releases all future rights and claims. Furthermore, it is imperative that his/her subs sign a seperate release because if the sub doesn't get paid by the General Contractor, rightly or wrongly, they too can put a lien on your property, I am not sure what other states do, but in CA, there is no policing of ML. If a contractor gets p---sed off randomly, a simple trip to the Recorders/Clerks office for $15 will make him/her feel a lot better.
Never has happened to me but I know others who had nightmares. Watch your title and get waiver releases at the end of each project from anyone who set foot on your property that ever picked up a tool!