For some, a roof mounted tripod and mast is an excellent mounting option. Chimney mounts or eave/wall brackets may be a better option for others.
When mounting more than one antenna on a single mast, a 5' TV antenna mast is too short to permit adequate spacing between the antennas. I have used 1-3/8" diameter chain-link fence top rail for the mast in several installations. Last I looked, all are still standing and in great condition. If I have no compelling reason to do otherwise, I put the UHF antenna at the top. This aids UHF reception in most cases, and the wind loading is usually less for a UHF than a lager VHF antenna. I try to provide at least 3' of separation between antennas, though more can make a noticeable difference in many cases.
I've not used guy wire supported masts in quite a few years, but would still consider doing so if I needed to use multiple sections of mast.
Besides the local big box stores, Frys, Best Buy and Radio Shack stores, there are many online sources for antenna mounting hardware.
A few are,
http://www.3starinc.com/
http://www.amazon.com/
http://www.antennacraft.com/index.html
http://www.antennasdirect.com/
http://www.channelmasterstore.com/An...ories_s/39.htm
http://www.solidsignal.com/
and many that I've missed...