had one built last year - I used redhill equestrian sand (v good quality but running short) and long flat rubber pieces as the surface - will find name and details - it is very very good. the surface is the most important part (its the most expensive single part and will decide how it rides. know people who have had sand put in that is not good quality and its a disaster! we use it for general schooling, cantering (fitness) and a bit of jumping. it doesnt track and needs v little maitenance. been using mine for 8 months and have not harrowed yet (gets used about 10-15) times a week! expect to pay £20-25 per square meter. many will quote much higher but its a rip off. my builder was very good and he was local to me but does advertise nationally. they are a proper drainage company so know the drainage part. finishing was not the strongest and they did do some damage to fields when it was wet and they promosed not to work but thats builders! very pleased for the money!
Mine's silica sand and rubber topping which is good as it helps retain moisture when it's very dry. Most important to get decent drainage because you'll want it to stay drained during the wettest weather. We seem to get extremes in this country these days! The company who did mine was Equus Arenas who, obviously, were experts. Once you have one, you'll wonder what you did without it!