Heavy gaming means desktop with some beefy PCIe video card. A multicore CPU is a definite plus as is a copious amount of RAM. You will also need a 500 to 750W PSU. (a 1000W PSU is overkill and only good for bragging)
Need good cooling!
Autocad, and about every modelers and graphics applications don't rely on the graphic card that much, they do most of their work on the CPU and main RAM. They almost only use the video card for the preview.
Multicore (4 to 8 cores) high end 64 bits CPU running a 64 bits OS is a must. Also, as much RAM as you can afford. With a 64 bits system, you are no longer limited to 4 Gb of RAM, you can have 24 Gb (triple channel with 3x8 Gb sticks) and way more...
This apply to EVERY modelers and ray tracers, although there are presently some GPU based ray tracers, they are still mostly at the proof of concept and alpha stage.
I don't know Revit, but as it's another architectural application from Autodesk, it's demands should be similar to Autocad's.
Recomended, not minimum, hardware requirements:
Microsoft Windows 7 64-bit Enterprise, Ultimate, Professional, or Home Premium edition
Intel® Core™ i7-2600 (or later) quad-core (hex or octo-core if possible) processor (3.8 GHz, 8 MB cache ) or equivalent AMD processor
16 GB RAM (or more)
Electro
March 2012