Would House Rowan of Goldengrove need the permission of House Tyrell to build a ring road like you suggested in your Economic Developments series? Or could they do it on their own while giving their liege lords a heads up about what’s happening?

I don’t know whether you need permission to build a road (as opposed to building a castle, where you definitely do), but my guess is that House Rowan would need the permission (or more likely, a license) from their liege lord to build on lands other than those of themselves and their own vassals. 

So in the case of a ringroad meant to connect the Ocean Road to the Rose Road by way of Goldengrove, at the very least you’re going to need the permission of the Oakhearts of Old Oak, quite possibly the Cranes of Redlake (depending on how far south their lands go), and definitely the Caswells of Bitterbridge, and given how large those open plains are I would guess some more houses.