For a new build (building yourself I presume you mean rather than buying one) you'd mainly need to do market research...
Check land prices and ensure you're paying a fair (or below!) market price. Remember you make your profit when buying. Built to your well researched target market in the right location for that market.
Make sure you carry out title checks and searches (your solicitor will do that level of due diligence for you). Carry out due diligence on each of the building contractors you plan on using and ensure you get a solid contract in place (e.g. A JCT contract) with penalties for late delivery etc...
Hope that helps