I would like additional shapes and the ability to place them in any orientation (look at space engineers for examples).
For example, there should be a corner ramp piece. This piece would be 8x8x2 and would have one high corner and 3 low corners. This would allow 2, 8x8x2 ramps to join to the corner piece (there should also be an 8x8x4 corner piece). Other shapes could include 8x4x4 or 8x4x2 blocks and ramps.
All the foundations and ramps should at least be able to be inverted (and maybe placed vertical). I make elevated roads for my vehicles and it would be cool to smooth the bottom of the road by placing an inverted ramp on the underside of the road.