This suggestion is maybe a mod topic. Wouldn´t it be great, if there would be a drawing board, where you would be able to design your own buildings? If you activate it, you can plan your custom building in something like an editor. You have to check statics. The costs would depend on the blocks, doors, roofs etc you implement in your building. After that you can draw your own architecture plan and you will receive it as a document in your inventory. With this you can set the building site and build it like the fix implemented buildings.
I don´t know if something like this would be possible. I don´t know if something like this should be just cosmetic or should be able for barns or stables etc.