I've always considered the term 'trews' to refer to later 'trouser type garments' (c.16th - 19th C, eg the dungiven, the cotton trew, etc etc), rather than something medieval, which is why I asked for more info.
But it struck me that you might be looking for medieval "trousers", which were worn in the further reaches of Europe, insted of hosen (meaning Ireland, northern Scotland, Scandinavia) and by the peasant classes in the more central areas (England, France, Germany, The Low Countries, etc).
If you are looking for medieval trousers (rather than hosen), stay away from the hose patterns, because they're completely different in cut and construction.
Trews were the natural evolution of your older hose
Sorry, but they're not as it happens (though that's the natural assumption, and one made by costume historians for years).
Till Janet Arnold and a couple of others got involved. The cut is actually more likely to be a combination of the split hosen (meaning single legged of the early medieval type) that were still worn in some parts, and the 'trousers' that were worn in others.
If you look at what's known about trews, and compare it to what's known about hosen, the cut of the two bears hardly any resemblence, although looking at a pair of each made up, you could barely tell.
I'm not sure that there is a medieval trousers pattern anywhere, but I'll have a think.