The Hell Barn simply looks like a barn with its front half charred, but there could be a backstory to this too. It is said that the Epsilon Cult were famous for their desire for burning things, which puts it in the conclusion if Rockstar added this as a reference to them or not. There are two identical burned barns in that location, but the similar use of this texture was never seen anywhere except here. The Hell House could be connected to the barn.
Though it is true that the farm is a lot further away from the barn's location, there is another explanation for this. Most likely, lightning could've stricken and caused a fire around here that must've caught both of those barns.
Some players confuse this barn to be the barn in Are You Going to San Fierro?, where CJ burns all of The Truth's marijuana plants before the police arrive. Some think that when CJ was burning the weed, the fire could've theoretically reached those 2 barns and burned them half without anyone noticing, but the fact that this is a totally different barn proves this theory as false.