York Modelmaking was an architectural model business with a sideline in bespoke work for people like us. This grew so much that the model rail side appears to be a separate business, with a lot of "standard" items such as lattice-work bridges, window frames etc. They still appear to offer a bespoke service in wood and plastic. I used 0.8 mm ply for sides, panelling, window frames etc, 3mm for ends and partitions and 5mm for the floor. I have not used MDF. For reinforcement and the roof I used spruce strip from Hobby's. I wrote an article on the process which was published in GardenRail for April 2013. I might still have it on a memory stick somewhere-if I find it would you be interested?
John