I currently have a concrete slab patio thats 10ftWx20ftL. No roof. I wanting to add more living space to my home its concrete slab drops about 4 inches from house foundation. Also my garage is 18x20. It has a drop of 1.5 inches and slopes to 4inchs at the garage door. Either way I will need to have concrete work done depending on what i decide the patio or garage for addition living space. my questions are on patio can i just add more concrete to make level or it has to be new slab? And garage whats the best way to make the house level either way I dont want a step of any kind any my home i want it all level.