Back again.
I would suggest at least 12' tall lower side, even if the current RV is only 11'4" tall at the center. Lets say that you need to patch the roof, and you wanted to work on the roof. How can you do that with a 12' tall roof, where you barely scrape the roof as you enter?
So if you have a lower wall consisting of 4X4 pressure treated 12' long sitting on the cement that the RV will park on, install a 4X8 or 4X10" on top from front to back, then rafters sized for your local snow loads will sit on top of this. So it will be at least 12' 7.5" to the bottom of the rafters on the low side, and up to 5' taller on a 14' span to the higher side. So you would be able to work on one side of the roof, and then need to turn it around if you wanted to work near the edge at the lower side of the carport.
Make sure to get a permit to build something like this. The plan checker for your county or town will make sure that the snow will not crush your RV and damage it. You might be surprised to find out how much weight your roof (of the house) must support. But lets say that you get 12" of snow followed by 3" of rain. Some will worry about the roof caving in, but if built to code, yours will be fine.
You might also want to consider a metal roof. It will help the snow slide off better.
Good luck!
Fred.