Welcome fran, generally speaking a 45* angle works pretty well. If you use OSB you might have to put a layer of tile board, or create a smoother surface to get it to slide easily to the auger.
The doghouse design found in the Axeman Anderson manual works well (you can use the search function to find it), as long as you can pull the auger back from the bin to work on it. Otherwise you will have to devise some kind of removable section to pull the auger out sideways. In any case you will need to prevent the coal from spilling out of the bin by sliding a door in place.
I'm sure others will chime in with some practical suggestions. Keep us posted as you complete your set up.