Go paper, there is loads and loads of paper buildings to be found on Internet. Start, for example, on Brumbears site. He has some great models specificly done for warmaster. Use a slightly thicker paper then normal and you will have cheap, nicelooking scenery that will also lasts a long time.
Do you prefere to base your scenery...... create a nice base and the ruins of the building you want to have on it, dimensioned slightly smaller then the paper model, and just slip the "non ruined" version over it ...... this is also VERY handy when you want troops to be within the footprint of a building.
And did I mention that most of the stuff made available commercialy for 25/28 mm is easily tranmorhped into Warmaster usable scale by any decent printer ??