The front part and lower side is from the MRC Joes Power garage kit. I started with that and the wood parts just developed from there.

I covered the wood with sheet plastic. Not expensive sheets - go and buy cheap for sale signs. Cut them and super glue them over the wood for a smooth surface that is easy to paint.
The sidewalks are for sale signs plastic as well.

I think it was around 18 x 18 inches more or less.

This picture may help with the size - you can see it fits just a couple of model cars.

The side you see with the ratPiss sticker logo on it is removable for photos.

Sadly the garage was heavily damaged and I never rebuilt it. I would like to build another one - maybe a little different.

Made out of wood it was easy to carry to model events all as one big piece. (minus the model cars, figures, and some accessories).