determine the load demand, amount of air required, from the equipment provided in the workshop. account for a small amount of leakage (hopefully none), any sudden load requirements, any expansion of demand loads, etc. + a x% to ensure demand is being met.
there have been many postings in other forums pertaining to compressed air demand and pipe sizing criteria. please use the search criteria to investigate your query's and if a satisfactory answer is not available, post the question. we'll be glad to help out.
meanwhile, good luck!
-pmover