sounds like youve given it some thought id love loading at your yard when you see some of the farmers yards it makes you sigh and an easy job becomes complicatedMost straw trucks are either an 18m wagon and drag, or a unit with a 13.6m or 15.2m trailer.
When the shed is nearly empty you’ve either got to load / unload all outside and run to the back of the shed, or park the truck and load inside. For ease of use and safety its easier to drive in and turn than reverse in or out.
You need a concrete pad at the filling end, hardcore does inside the shed, so much cheaper to only fill from one end.
Running back and forth costs more in the long term so better to make it so you can turn a truck inside.
To do this with a 15.2m trailer you need 20m minimum, but at some point someone will hit the shed so you’re better off wider. This is where the 24m comes from for our sheds.
We debated going wider but then we wouldn’t be able to reach to fill them with a 535-95 in the middle so would be a waste. When full at the filling end you would then have a wider face spoiling too.