Advice on sourcing/negotiating materials at best possible prices?

[Matthew Banks]

I'm not trying to buy the lowest quality material, but to ensure I get the best price on material I buy.

-stone, masonry, framing, drywall, nails, sheathing, cladding, roofing

-wall & floor tile

-windows

-doors
-fixtures

-finishes (counters, cabinets, trim, paint, etc.)

So far, it feels like we're paying retail for everything, apart from the 5% discount at Lowes etc. Do I need to hit a certain volume to be able to negotiate better prices?