I'm getting ready to build this:
I'm using 2x6's for the top and 2x4's for the rest. I'm going to bolt it together with 2 1/4-20x4 bolts at each leg/horizontal point. I kept the height to the top of the BK low so that it would be easy to see in and make additions.
The HLT and MT are on 1/2 plywood or particle board. The MT is raised 3 1/2 inches because my MT has a port off the bottom instead of the side. I don't need to heat the HLT (at this time) because I have an on-demand hot water heater that gives me 175F water out of a tap in the garage.
I'm going to put the BK on cement board supported by the bottom horizontal 2x4's. I'm planning on bringing the black pipe out of the front and having the ball valve located on the 2x6. This is a 32tip natural gas burner that I have capped to 16 tips. I have metal flashing around the BK hole to protect the wood.
Finally, I'm planning on using 4" or 5" locking swivel casters to move the thing around the garage.
I want to get camlock fittings and silicone tubing for all my connections (either brewhardware.com or bargainfittings.com), 1 or two of these pumps http://www.homebrewtalk.com/f11/cheap-pump-fda-approved-12v-100c-337933/ and one of these plate chillers http://www.dudadiesel.com/choose_item.php?id=HX1220BWGH.
I should be able to get all the wood, hardware, flashing and black pipe locally (Menards) for about $120. The pump(s), connections, chiller, and tubing will cost another $270.