We are in the process of building one right now. It is a 80x100x20 with a 40x20 hydraulic and 22x16 overhead in the front and a 20x16 overhead in the side. We decided that we wanted plenty of access to the building and like you we really don't need to be able to get in with a 40' head. When we go to 40' heads we will have to take them off for most road travel so most times it will already be on a trailer anyhow if we run into that winter combining situation again. Otherwise, these heads come off in about two minutes now days anyhow.

Since we were building the building 20' high we did want one door with 20' clearance. We don't have 20' clearance for the full width of the 40' door but we do for about 30' of it. 41 & 43' Deere chisel plows are over 18' high in transport mode and I figured 20' would allow for most anything in my lifetime.

One suggestion I do have is that if you go with a steel building, put in an expandable endwall on the back side. That makes it much cheaper to add length or to add another door in the future if you want since the beams are already in place.