I'd have the valve located where the others have mentioned, where you can open the door and turn on the water without having to step into or reach through the shower head flow. If required for space, I'd consider moving the niche deeper into the shower so the valve can be closer to the door. I'd recommend having the rain head centered on your short wall. It can be centered or a few inches deeper into the shower on your long wall. I'd place two can lights in the ceiling, offset on either side of the rain head. I wouldn't use a built-in bench, or a built-in foot rest. I'd rather have a movable 3-legged stool. A stool can be used as a footrest, or pull it in the middle to sit under the rainhead, or if it drives you buggers move it out of the shower completely. Though I make them out of teak, they can be purchased too. Wood is usually more comfortable on skin than tile.

Some people really want/need an en-suite bathroom. Some people would like one, but can live without it if everything else--location, price, other amenities--fits their needs. Some people really don't care either way. And some people really don't want one. So if you buy this condo, you have eliminated the "really want/need" folks from your potential buyers and renters. But you still have a fairly large pool of potential renters and buyers to draw from. If you add the shower to the downstairs bathroom, I think you will make the condo attractive to non-related renters--three grad students, say. Do other units in the building have en-suite bathrooms? If so, then not having one could be a liability. But if there are other units without one, and the building itself is a desirable place to live, then you should be fine. You might have to lower your asking price to draw people in, but that would be the main drawback that I can see.

Thanks Mark. We have a nice portrait on the wall as you walk up the stairs as a focal point, but your solution is probably the best. You could do outswing, but have it rest 180* against the wall shared with the stairs. I didn't think of that at first (I thought, "Outswing it, so you see the open door when you come up the stairs,"), but since you have something nice planned at the top of the stairs, I wouldn't want to block something pretty.

@karibyrne I guess I don't understand what you mean by no vanity. The vanity I drew is next to the toilet as you walk in the room. The rectangle with the circle in it. The window drawn in for the staircase would be symmetrical with the window in the bathroom. Like I said, sketch was pretty rough. I'll try again with some graph paper today. Do you have the length and width of the overall addition. I think that would help so the drawing is more to scale.