Need Help With Logistics on Mobile Home Repairs PLEASE!

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We just got our first mobile home deal, and are looking for some guidance on working out the logistics of doing mobile home repairs. We are to instruct Contractors/handymen that we solicit to NOT include costs of materials in their bids, correct? So that means they are bidding labor costs only- based on the task. We (investors) price, buy, and deliver windows, siding, skirting, linoleum, carpet, floor boards, AC, etc. We then determine from repairman we hire what additional materials (nails, caulking, etc.) he needs per job and we buy those items and have ready at mobile home also? Bottom line: the investor buys all materials needed and delivers to the job site? And most importantly, we pay by the job, NOT the hour, right? Do we have this correct? All advice and tips are greatly appreciated!