I'm planning a new sewing room too, in our attic so I have the same issues with sloping ceilings etc. So I'm following along and getting some good tips from everyone here! :-D
Something that I'd like, as well as the 'flow' that Mad mentions, is some kind of L-shaped arrangement to the left of where I sit at my machine, so that when I'm putting on a border, quilting or binding a large quilt, it can carry the weight of it. Ideally I'd like this to slide in and out from under the desk but then come up so it's on the same level. My DH LOVES these little challenges I set him! :mrgreen:
I'd thought of putting my main desk along the wall under the eaves - mine start at around 3' from the floor, but making it double worktop width, ie 4' so that large quilts will have plenty of room to back up. I figure this is dead space anyway because of the head banging thing! I saw on Leah Day's website that she recommends this space behind your machine when quilting rather than an open backed desk where the quilt goes over onto the floor.
Sorry to be so long-winded - brevity is not my strong suit!