you mean like one of these (link)?
Why not just make it out of a square tarp, but don't sew it together into a tube, just use one side as the bottom? These have the disadvantage that if rain gets in one of the ends, it's not getting out. But if you did it as a square tarp, then you'd have the option of a more appropriate pitch for the weather. By placing mid-length tie-outs on top, you'd have pitching options to do a tube tent with doors, or you could use as a flat tarp with an off-center peak.