In your case it will be impossible to hand window treatment at the same height. Maybe if you use different treatments, for example a roman shade on one and curtains on the other, it will make the windows seem intentionally different elements rather than a mismatched pair?

If that were my house, I'd be tempted to remove the upper trim from the taller window so I could do some type of roman shades or woven wood shades at the same heights. How much is it off? It's hard to tell from your pictures. Another trick to mask the short slanted wall is to paint the sloped ceiling the same as the wall color.

I would mount the curtain rod for the short window as high as possible and the one for the tall window at the same height. Then I'd mount roman shades, right under the rod, so that the bottom will barely cover the top trim on the shorter window. Then hang the other shade (which would be the exact same size) mounted so the bottom will hit at the same level, but will actually cover more of the window. They would have to be opaque for this to work. And to get all the hardware to fit, you may need to remove the trim on the top of the taller window, as was suggested.

So they each would look like this, hung so they look identical, but the larger window would have a bit more of the window covered, the shorter would be covering the wall above it, making it look like it's the same height as the taller one.

Thanks for the responses!

I would have to measure to see exactly how much they are off but, with the curtain rod as high as it will go on the short wall, the top of the rod at the same level on the adjacent wall falls below the top trim.

A friend of mine sent me these pictures from Houzz that don't look too bad.

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I suppose I will have to play with a few different arrangements and see what looks best.

I'm with tinan....the fact is the windows are very different in height so treat them with the same fabric but in different styles....

I think the houzz examples look fine, but their "short" windows are full height whereas your short window really does look short so it needs a treatment that will look more in proportion with its size. Maybe just a valance on the short window and side panels with or without a valance on the tall one.

I'd just hang drapes that fit each window and call it a day.

As you can see from Houzz, it's fine for a window in a knee wall to have a shorter treatment than the gable wall. I would adopt the trick of using a wall-mounted Roman shade to visually lengthen the short windows, although you are not going to get it to line up with the big window, ever. Don't even try--better to be distinctly different than just off. And no, do not wreck the window trim for a curtain!! Do people think there's nice paintable drywall behind window casings??

Thanks again for all of the feedback!

The room is becoming a bedroom so the window treatments will be as much for privacy as for decoration so I'll definitely be incorporating a shade. I kind of like the idea of different treatments with the same fabric so I will play with that!

And removing the trim was never an option! ;-)

I agree with yayagal....hang to fit the windows and forget about it....I do think the curtains/drapes should be the same for both windows....not valance/drape but drape/drape.