Be sure you know your goal and if possible speak with him before purchasing parts outside of a camshaft. He will tell you if something isnt right or ideal like header size or a intake for example.
probably most important is once everything is set in stone and the cam design and build process gets rolling dont go chnaging your plans or switching parts on him. Too many times has he had past customers unhappy only to find out the parts they used were not the parts disclosed on the buildsheet. Not at all saying theres alot of unhappy customers, just that the ones that were usually weren't honest with their combos make-up.