This is just a quick post. Since I scratch build a lot I have always been on the look out for building plans. These apply to my era but some of them can apply to new more resent eras. Now not all these plans give you every measurement but you can easily fill in any blanks if needed. I redrawn some plans from these sites, I just haven't had the time to build them yet. They will get built as I, work my way through the rest of my scenery.
North Dakota State University Has a lot of farm building, tools, livestock equipment, grain and some house plans. You will notice in one column the year the plan can out.
Colorado State University This also has a lot of farm building, tools, livestock equipment, grain and some house plans. You will again notice in one column the year the plan came out.
Sears House Plan Archives This one is interesting if you are looking for older house plans plus you get some history about Sears also.
Shorpy Photos are just really nice pictures that can show you details of older eras that you would not normally get to see.