We are working on a large masterplan with a number of different buildings on site. WE are going to build each of the block in a separate file and reference them into a 'Master' Site plan. However, as the site has overall a 5m height difference across its length, the buildings will be 'stepped', i.e. they won't all have the same 0.00 level. but hey will be staggered, to meet the existing contours. My question is how, once referenced inc an I decided the equivalent 0.00 point for each building (which would the be the actual Datum given by a topographic survey.) I cannot seem to find an answer anywhere but I am sure its a problem many have encountered. Thanks in advance.