I believe a cellular blind would look better. You can push them all the way up so that it only takes up about an inch or so when mounted inside.

And with roman blinds, even if you mount them on the outside, when You pull them up, a portion is still going to cover the top of the window. I mean, how high above the frame do you plan on hanging them??

these are in my sons room. when pushed up, it really doesn't block any view.

blinds look cleaner when mounted inside, with a nice casing around it.

you could do outside w/these if you like

the other option is to use Silhouette type of blinds, they allow you to keep them down, but 'open' so that you can still see outside. I used to have these in a sheer white and loved them.

Sonnette Roller Cellular shade