You could probably do it (whether with core buildings or regular buildings) using the "and not building_x" conditionals for the building requirements.
e.g. If your four tech-tree buildings are "Building_A, Building_B, Building_C, Building_D", then it might look like this:
Code:
Building_A requires factions { zulu, } and not building_present_min_level Building_B and not building_present_min_level Building_C and not building_present_min_level Building_D
Alternatively (and probably more simply), you could use temples. The existing temple buildings seem to be hardcoded such that there can only ever be one line of temples in a settlement. So if you simply rename some temples and give them the stats that you want for the building, that should give you the effect you want.
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