Each pen needs to have at least one cat cabin, more if more than one cat is sharing a pen. The side rooms needs several cat cabins as they are frequently used to house multiple cats, each of whom needs their own private space.
Buy or have made (depending on cost)15 cat cabins.
Potential for using Ikea Kallax in the larger rooms, as several brands of compatible insert cat cabins already exist.
3 stand alone cat cabins for new pen in main room.
6 stand alone cat cabins, or two sets of Ikea Kallax 4x2 and 6 cat cabin inserts, for side rooms.