All of the track builders mentioned are professional track building companies/businesses, and I got the impression from Willy's first post that he was looking for tips on track building, not a company to build the track for him.
Biketrack (run by Steve Taylor who rides for my BMX and 4X team), Clark & Kent and Jason Carpenter are all brilliant track builders, but the tracks they build all require a reasonable budget. I'm not sure Willy's project has such a budget.
The best tip I can give if building a track yourself is put some decent drainage/stone layer under the top layer to stop it getting flooded. Also, use crushed stone on the top surface to stop it getting worn out when ridden in the wet.
Good luck!