Rough Percentages
Archetypes take up 5% Minimum
Lands take up 8.33% Minimum (30 in a 360 cube), but usually include more.
Gold cards take up 8.33% (30 in a 360 cube)
Colorless cards take up 8.33% (30 in a 360 cube)
Removal runs from 15% up to 30%, depending on the feel of the cube, and usually about 2% wraths. I would say the more efficient (better) removal is the less there should be overall. I'm going to include temporary removal in this count, unsummons, taps, etc.