Adding to what Steve said: It’s best to think of every building in terms of Gems, not Building tokens. If you want to convert, 25000 BT = 1 Gem.
I’ve attached a table for all the buildings. The important thing for building or upgrading monuments is NEVER OVERSPEND.
You can use any combination of buildings as long as you exactly match. For example, if I get a level 4 building as a reward (10 gems), I need 90 Gems of buildings more to convert to a L1 monument. So I build 2 level 5, 1 level 6, wait at least 4 full days to take advantage of HMP, then convert to L1.
