When editing a roof or a floor by points, we have to know that Revit will deform the objects affecting their thickness.
So, if you want to use this tool to obtain something like a simple two slopes roof, keep in mind that you're introducing a really stupid mistake in the model. Soon or later it will appear.
Spend more time on learning how a tool works before you use it.
Try to get the same thing using the massing tool and you'll appreciate a perfect model in a short time.