Yeah, papercraft templates are the way forward (even if you don't actually use card - you can still print the templates to make buildings from
MDF, foamboard or whatever). Just google 'papercraft fantasy buildings' - that should give you plenty to work with.
Also, if you don't mind paying a few quid (or dollars) then checkout guys like
Dave Graffam. He makes some really cool buildings that you can print out and make. And remember that once you've purchased a template, you can print it as many times as you like to make as many buildings as you care to.