Most Roman shade mounts have holes in them so that they can be mounted on the inside or outside of the window.
Just mark the location where you want to mount them and place them as you would on the inside of the window.
Be sure not to place the mounts too far away from the outside edge of the windows or else they will bow on the ends if they are very wide shades. 52 inch or wider. With-in 5 or 6 inches of the window edge is good for wide shades, but if the shades are narrow, (such as 23 to 26 inch or so), then you can place them close to the corners of the window edge. About 1 inch from the edge is good.
Just mark the location where you want to mount them and place them as you would on the inside of the window.
Be sure not to place the mounts too far away from the outside edge of the windows or else they will bow on the ends if they are very wide shades. 52 inch or wider. With-in 5 or 6 inches of the window edge is good for wide shades, but if the shades are narrow, (such as 23 to 26 inch or so), then you can place them close to the corners of the window edge. About 1 inch from the edge is good.