Construction Question on Square Trailers

My question involves the Grasshopper type of trailer. Actually any squared off trailer.
For those that have built one... why do I notice that one common denominator for these trailers is on the front wall. Instead of a 90 degree roof line/front wall interface, there is an angular offset of varying degrees. Is this necessary for some reason? Some are quite extreme and some are very slight. I realize this has more of a pleasing asthetic line to it, but is it structurally required or easier to build?
The reason I'm asking is because I am going to build a 5X8 box type trailer and have worked through most details now except for this front wall roof interface.
Thanks for any input.

For those that have built one... why do I notice that one common denominator for these trailers is on the front wall. Instead of a 90 degree roof line/front wall interface, there is an angular offset of varying degrees. Is this necessary for some reason? Some are quite extreme and some are very slight. I realize this has more of a pleasing asthetic line to it, but is it structurally required or easier to build?
The reason I'm asking is because I am going to build a 5X8 box type trailer and have worked through most details now except for this front wall roof interface.
Thanks for any input.
