Had a tuxedo female show up at the farm and mom has taken to it. Mom never was a cat person but 'Pretty Girl' has won her over. In cattlemen terms, she now is apparently a 'heavy springer'. There is an storage building that has seen its better days and is on the demolition list due to its door falling off resulting in the floor giving way at the entrance. She has taken up residence in it since it is dry and warm.  The problem with that is that I'm digging the crap my father left in there(think almost hoarder level BS but old farmer stuffs), and getting rid of the trash or moving the tools over to the good shed. So, no place for kittie on the right side. Left side is mostly open and requires no gymnastics to get boxes out.

Want to get/make something she can use for the kittens but be secure enough to keep vermin out. Yes, I still got the 16 gauge pump.
Suggestions?

Big cardboard box with old rug, straw, and/or newspapers in the bottom, put it on the side and make the box flaps into a kind of porch if she has kittens to keep contained. Cold weather can wrap the box in bubble wrap for insulation.

Build a box. Put a curtain in the doorway. Then add a seedling heater mat for cold nights.
Not rocket science.

Here is an idea. A bit involved but kitty might really like it. Or a possum. Maybe a raccoon. Honey badger.

Cat House

A plastic tote...turned upside down and cut a hole for entry/exit. Some straw, old blanket, rug, etc.

Look at the local Humane Society for a TNR (trap-Neuter-return) class. Will help a lot. At least it did for me.

My wife does something similar for the farm cats, except she uses old coolers