[ijames]

Well if the bed is 12' long then you could make the aerolid in two sections so when you stand them up in front of the building they are a reasonable height. See what aerohead says, but you could have the first section angle gently at say 3-6 degrees for 5' since the front of that is attached to hinges to the top of the metal hoop so when you stand it up it will be about 2'+5'=7' so it just covers your building cargo, then have the second section angle at 12-15 degrees for 7' so when it is vertical it goes from the bed up to the top of the front section. Either have the two pieces joined with a hinge or have them join with something like hasps and clevis pins.

The way to think of the aerolid design is as a box with angled top and narrower at the rear of the bed than the front, with side panel and an end plate (either flat or the pvc pipe idea), then when you need to carry cargo you flip the box vertical to expose the bed for cargo and to form a wall in front of the cargo that you can add rounded top and sides to.