I'm new to making buildings so if you think other sizes (wall height, door size, etc) would be helpful, leave a comment and let me know. I just made this 1/4 inch taller to help accommodate the variation in scale of minis.

This is a small bunker that should work for human size characters in the 25mm to 28mm scale. I did this in inches rather than metric and the floor tiles are 1 x 1 inch and the walls are 1 x 2.25 inch panels. The door opening is 1 inch wide and 1.75 inches high. with the roof, the total height is 2.375 inches. The roof also has a 1 inch grid.

If you want to play with the pieces I designed, here is the Tinkercad link https://www.tinkercad.com/things/jQFeIHsGCfu-bunkers-1-inch-scale
You'll find all the pieces I used to make this as well as a couple I didn't use. The roof is assembled from 3 different tile types, a center, edge and a corner. The corner pillars are there to hold the roof in place. Make sure the grid is in inches and everything should snap into place. Change the "Snap Grid" resolution to fine tune the positions.

Tronxy P802MA

No

Yes

.2mm

15%

You'll most like need supports for the windows and door.