I want to dig a new garden in my backyard. I have an area just off of my brick patio that slopes down about 1 foot over the length of 8 feet where it gets flat and goes out to the back yard. I want to utilize this space as a garden because it will be easy to access and easy to mow around. The problem I have is that when it rains and all spring long the water pools around the bottom of this slope. Should I build it up all around this area and wall it in to make it level? What should I use in the bottom of it below the soil?