",,," wrote:

it sounds like they are decorative styles over plywood or other
construction instead of a plain 'Five V' roof on perlings and rafters.

The Collaborative International Dictionary of English v.0.48 (gcide)
Purlin Pur"lin, Purline Pur"line, n. [Etymol. uncertain.]
(Arch.)
In root construction, a horizontal member supported on the
principals and supporting the common rafters.
[1913 Webster]


Yawn. I knew it was wrong, but it was close enough for you to
complain, wasn't it? It wasn't in the spell checker in this program, and
I really wasn't going to waste time looking it up. I haven't had a
decent night's sleep in over a month and I don't give a damn.


--
It's easy to think outside the box, when you have a cutting torch.