There I am again, with a scan of the plan. There's some measurements beside it. I guess the window holes are slightly smaller, but you nailed it very nicely allready, Cyphyr. The roof was actually made of lead, strips of it overlapping eachother, but that's too much detail I guess. There's one more middle rib/ridge from the rooftop downward in the middle of each of the 10 top sections, and also in each of the 20 lower roof sections, as you can see in the detail.
There's also an unobtrusive ornamental ridge just below the higher roof, but it's not clear how that looked. And I don't know how to interpret the spiral staircase housing that can be seen, maybe forget about it or think of some easy attachment. At the tower front side there's probably a big door. In the outbuilding there's two adjoining windows within each arch at the three sides. The windows are just holes, it was 1100 AD after all.
I hope you have enough information. Let me know if you don't. Many thanks, I'm much obliged for your effort.
Will you post the obj or mail it personally?
---Dune