Here are the lengths of aluminum rails I used for building my 3d printer.My final dimensions were 315x290x295 I could probably get the full cubic foot by adjusting end stops on my machine, but if you want the full bragging rights you may want to tweak these lengths.

This the rail I used: http://openbuildspartstore.com/v-slot-linear-rail/

Cuts for a 12″x12″ heated Bed

20×40 Rails
A. Legs x4 = 515MM (2x1500mm)
B.Horizontals x4 = 440MM (2x1000mm)
C. Top Beams x2 = 450MM (1x1000mm)
D. Base Beams x2= 430MM (1x1000mm)
E. Bed supports x2= 395MM (1/2 x 1500mm)
F. XY Slider x1 = 464MM (1/2 x 1500mm)

20×60 Rails
G. Z Slider = 428MM (1x500mm)

Z Lead Screw x2= 400mm