I am not thrilled either. Basically, I think the bay window is completely unnecessary both downstairs and upstairs. It has no function and certainly cannot be furnished; so it is just a cost factor. Without views, though, it's hard to say. By the way, if there is going to be a guest room, then also a bathroom with a shower on the ground floor. Or are the guests always supposed to shower upstairs with you... :p A knee wall of 1 m is actually normal, why should that cost more? Hopefully, you have obtained comparative offers. To be honest, the longer I look at the floor plan, the more I agree with Mycraft. Not only is the upper floor with this bedroom (terrible like that, better to remove the bay window and make the children's rooms the same size!) unacceptable, but the ground floor is also not acceptable. Much more can be made out of it. Take a look at other example floor plans on the internet.