Don't know of any sights that will provide that much information for you. I'm sure many of us here at armorama would be willing to help you through the design and building process if you can give us some idea what you want to build.
There are really no hard fast rules, many of us here scratch build our own buildings and from many widley availble materials. Size and dimentions are all relative. My first suggestion would be to have a look around Roadkills reference gallery here:
http://photos.kitmaker.net/showgallery.php/cat/626I might also suggest looking at the Verlinden and Custom dioramics diorama products for ideas.
Choose your subject/region you want to model. It will be much easier for us here to help you realize your goal if we have a better understanding of what you want to build. Once you choose your subject/s find a photo or come up with a drawing to show us ... Then we might be able to give you specific ideas of how to make your own "blueprint" for the buildings you desire.
Paul