Glad my rambling thoughts were interesting (to someone other then me!).
Those plaster ruins look good - I think the ones called Fionn and Daena would fit my notion of elven buildings best, but they're all good - though I don't really care for the towers.
How robust they would be depends a bit on the sort of plaster they're cast with. I use some stuff called Keramin to make Hirst Arts blocks, and it's a good deal less fragile than standard plaster of paris. Since these are made for gaming, you'd hope they'd use something fairly solid...
I had a look in Tuor, btw, and as well as a detailed description of the seven gates of Gondolin, (probably not much use as a guide to standard buildings, but fun) there's an interesting description of Turgon's abandoned hall at Vinyamar, "eldest of all the works of stone that the Noldor built in the lands of their exile". It's incidental to the action rather than a set-piece description, but there are some hints. So, we have "the coping of its walls" and "the great shingles of its roofs", and overall "the old hall and its high and windy courts" set on a terrace, with a west door with a "mighty lintel" at the top of "wide stairs". Beyond the door, there is a "high-pillared hall" with "at the eastern end a high seat upon a dais". There is a paved floor, and "pillared aisles". There is also "a high window under the western gable".
So far, I suppose, so generic; but I think it's clear that what Tolkien imagined was a fairly conventional early medieval hall, albeit on a grand scale (with internal pillars and aisles) and in stone rather than wood, rather than anything more elaborate in its plan at least. Perhaps something a bit like a late Roman basilica (like the one in Trier, say) might be the closest analogy? I'll let you know if I come across anything else that might be helpful.
Looking forward to seeing where you go with this.