I am planning to build a small greenhouse (ish) between my house and a boundary wall. For a raft of reasons I cannot put an ordinary green house in that space. I intend to use Corolux corrugated clear sheets. I am confused about the wooden frame to which I will attach the plastic. I assume the purlins will run at right angles to the direction of the corrugations. And that will mean I have to install wooden 'beams' between the wall and the boundary wall on which to mount the purlins. Is that a statement of the bleedin' obvious, am I over-engineering this or something else? Thanks