The base is 3mm MDF, cut to fit the same 10x10cm grid that I use for all my buildings. In this case, it's a 20x20cm base, giving a bit more room to play with. It has been designed so that if/when I make other buildings, they can connect together into a larger complex as desired.
The building itself is constructed from plaster blocks cast from Hirst Arts moulds. Although designed for 25-30mm scale miniatures, they still look pretty good with 15mm figures. I use parts from these moulds for a lot of my buildings. Some are almost completely built from plaster blocks, but others are mainly foamcore, card etc. but with the odd clock added to represent ducting, plant & machinery and other functional looking items, adding character to the buildings without too much effort.
The doors are removable - the top of each doorway has been left separate, enabling me to lift it off and slide the door out.
The yellow "Dragon's Teeth" at the front are intended as a safety feature as found on many modern industrial buildings - large vehicles entering the garage at the wrong angle would hit one off these first, rather than colliding with the wall of the building. They also provide a handy bit of cover for anyone defending the building from attack.
I need to cast a few more blocks; I was using up some of my existing stock, and ran out part way through construction!
There will be a first floor for the building, which will most likely be made from foamcore.