I don't think you need a ramp or to lower your roosts. Or even add the window, (but today, I wish I had a window -20 and bright sunshine).
If in the daytime they are all over those roosts, they KNOW they are there. My own roosts are closer to 4 feet off the ground with a bench about 2 feet off...
Well I don't have windows in my coops, so unless you want a window in your coop no need to add one now. I don't turn on a light at dusk either, and my roosts are about 4 feet off the ground. I do not think there is anything wrong with adding those things if you want, but not sure about...
Did they ever roost?
I admit, I am quite surprised they are not roosting. One of the big problems with a flat surface or sleeping in the nest, is the poop does not fall away, and they tend to get dirty. You said they roosted outside, so they know how to roost.
From the picture, it looks like...