I really don't see an issue with the rooflines. Looks like the angles are fairly similar and the clean lines of both structures should be easy to coordinate, especially in your open, rural setting. Since you've found a stunning deal, I would say, go for it! I definitely would want to find an architect ASAP and by all means, before you pour the slab, make sure you have a plan to coordinate.

Kind of funny really how many people would feel exposed and would not want to use the bathroom. The more I think about it, it's a bit like a public restroom with stalls (as stall walls rarely go to the ceiling or floor and have the added issues of gaps between the wall panels and doors -- which thankfully we won't have!). Regarding the humidity control issue, I should have clarified this is only for a toilet and small hand basin (not a full bathroom with shower). The main room on the other side of the proposed toilet is our dog whelping room where we will have young litters of puppies (when we have them). Further down the hall, removed from this room, is our training room where there are likely to be other visitors but the proposed bathroom would be quite removed from that area. It would be wonderful to find more windows like the ones that are up near the ceiling! That would certainly solve the issue. I'll have to scour the demolition/restoration places.

OK - I'm a beginner here on Houzz so my opinion isn't worth a lot but here it is: the room is a bit bland and lacking in character. I think you have to find some pieces you really love to bring it alive. All the suggestions are good for widening your horizons, but ultimately, you need to find things that matter to you, because it's your home and not a magazine photoshoot. That said, if it were me, I'd throw a couple of small, colorful rugs down, and put either one large painting or three smaller ones over the bed - not in a line but at different heights - to break up the binary look. I'd also put something on the wall above the heater. Then, play around with a few cushions and maybe a quilt that picks up some of the colours in your artwork.

Thanks very much for all your feedback. Just to answer a few queries - the deck is directly outside the main room so the new doors open out onto it. The doors won't be French - they're just the only doors that the 3D planner I'm using had, they'll actually be large stacking doors. I've had another idea too which would be a lot more expensive but offers a completely different approach. This is quite rushed so doesn't show accurate layout of kitchen or anything like that, basically just provides an idea. Thoughts!?