NTBF – New buildings for the towns in Tribes of the East 3.1.

I don't remember the fourth game very well.
Could you explain?

And suggest a building?

Allow me. In the fourth part, you could only choose one building out of two available for hiring creatures of each level (except for the first level). For example, in Necropolis (undead and demons), you could choose between ghosts and cerberuses, vampires and poisonous horrors, devils and bone dragons.
In the upcoming seventh part, this mechanic is also present, but partially and only applies to higher-level creatures (champions).