If thesaurus construction is something that comes up only occasionally in the course of your work you should bookmark this tutorial created by Dr. Tim Craven of Western Ontario University for his LIS students.
Eight sections take you quickly through the basic concepts and considerations for building a thesaurus. It’s a handy refresher that is software agnostic.
In fact the section headings would make a good outline for a set of questions to ask the software vendors if you are considering purchasing a thesaurus management system.
Speaking of thesaurus software, Dr. Craven also has a handful of freeware programs to assist in indexing and thesaurus construction. I haven’t checked them out yet and so can’t offer an opinion.