I think height should be linked to both terraforing ability and resources used.
eg.
An entry level terraformer can build a 1 ft terrace with dirt.
A high level terraformer can build a 6 ft terace with dirt, stone and mortar. Possibly using a specialist tool like a brick hod.
Mortar could be made by gathering something like lime or bitumen.
I like the idea above that terraforming could be more closely likened to landscaping. This would help to allay my fears that terraforming in its current state is going to be a blight upon an otherwise attractive landscape.