Piping materials can be any of the following, copper, PVC, PEX, steel.  We purchase from local vendors that have showrooms for you to browse through.  They have different settings for kitchens and baths grouped together with a large variety of faucets and fixtures.  Unlike the "Big Box Stores", these showrooms have qualified design personnel staff that know the business, trends and needs of today.  Another big difference between a plumbing supply vendor and a big box store is the quality of the fixture.  The big box stores order "builders grade" and we get professional grade products. They might look similar but they are different, especially when you look at the quality of the material.  When you purchase through your contractor, we are responsible for warranty, delivery and on time installation.  If you purchase the material, you are the responsible person and any delays will cost you additional money and delay the project completion.