The arms that support the roller on the outside wall of the S/O only extend outward from the edge of the S/O's roof so far. So you really cannot use an awning that is a lot wider than the slide itself.
When you order the unit, they will have directions on sizing. You'll want to follow those to the letter.
I have installed several of them and still believe they are a good idea unless you only camp where it's very windy.
Also, by adding it yourself rather than buying it with the RV, you will probably end up with a much nicer unit. The manufacturers have access to really junky models that you and I cannot buy. I have two of those junkers on my new trailer!
My one piece of advice in installing these is to do so with as much of a slope as is possible. They shed water, wont "pool" and work far better that way.
