Bulldozing and grading are very expensive and the less earth that has to be moved, the cheaper the final project will be. While the heavy equipment is there, you may need to include the installation of some ditches to divert surrounding drainage away from your arena. After excavation, the arena site will have to settle for six to twelve months, then be leveled periodically before you add any footing material on top of the base. Footing must be well-drained and of appropriate cushion. The type of footing you will choose will depend on your climate, whether the arena is indoor or outdoor and what type of activity you participate in.
Jumpers require cushion without excessive depth.
Speed events require a firm footing such as a mixture including stone dust. Reining horses do best on a firm base with a slightly slick top of sandy loam. Dressage and pleasure horses work well on a resilient footing without excessive depth such as some of the processed wood products. This will lighten and loosen the soil and increase its drainage while adding to its cushion. It takes about 250 tons of sand to provide a four inch cover in a 100 x 200 arena.