Its for my sward and estate management assignment, there seems to be suprisingly little on the internet, and most companies dont seem to willing to help students!
Choose your site carefully
Put in lots of drainage
Make sure everything is level and the drains are well protected from contamination by the upper levels of stone and surface.
Pick a surface which is practical and best suited to your requirements.
Horse and Hound did an article a bit ago on arena construction and surface options - try searching the archives?
I havent actually had any experience with them, but i am in the building trade, so if there are any questions you think I might be able to help you with, pm me