There are a number of model railroading magazines in the US that occasionally have building articles and plans. The most popular are Model Railroader & Model Railroad Craftsman but what you are specifically looking for may be hit or miss as far as the structure type is concerned. I imagine you can subscribe or visit their web sites to go over past issues for the plans you seek.

There are also a number of books that have these plans that you can purchase. I suggest you try the Walther’s web site in the US to get an idea as to what is available (there’s quite a few). Unfortunately, these aren’t free but I doubt you’ll be able to find many plans that are free on the web these days.

One approach I have done is taking a camera and measuring tape and actually visiting a structure I’d like to model. The photos will provide details such as window or doorway construction and the tape measure will provide actual ‘hard’ measurements to base you model on.