I have an existing poured concrete patio that I am enclosing and here is my problem. The existing concrete slab is not level and actually slopes slightly in towards where I want to construct a wall and creates a puddle of water each time it rains. How can I slope the concrete away from the wall without busting it all up and re-pouring it? I can't create a step up approach, also the section will be exposed to the weather so what materials can I use that will hold up to sun and rain?

You might be able to have a company do some concrete jacking, check the yellow pages.

Put in a trench drain between the patio and the wall.