Space Consumption for SQL Index Rebuild
Typical wisdom is 1.5x index size, plus a little fudge depending on fill factor and how full your current index pages are (in most cases I would expect it to be slightly less than 1.5x). But I would definitely not cut it close. If you don't have 150GB free on your drive, I would find a way to do it elsewhere. I don't know if WITH DROP_EXISTING will help here, somehow I don't think so.