I'd just attach it to the brick wall below the gutter line. You shouldn't have any issues with leaking due to the overhang and gutter above. With that said 4' is really shallow and if you don't put a gutter on the new roof the splash from the runoff is going to wet most of your area. I'd go 8' out and get enough depth to fit the pits plus a lawnchair and a cooler out of the elements.