Get a hold of discarded but clean and sturdy packing boxes.,
Clean the boxes out by wiping with a dry cloth.
Secure the dividers into place with tape.
Draw or outline the shape of the entrance and exit into the side of the box.,
Close the lid of the box.,
Cut out the outlined exit and entry holes.
Repeat the process with all your other boxes.
Stack the boxes into a pleasing but not too tall formation.,
Introduce the cats into the apartment and see how they like it.
You can easily find this at supermarkets and local store. Some boxes have dividers inside in order to keep the items they stored snug and stationary during transportation. Do not throw away these dividers.;
,,, Make sure you position the entry and exit between the dividers so you do not accidentally cut through them later.
, Tape securely with a double or triple layer of tape.
,,, Tape securely at the back.