Compensation for design and build investment

Hi so I’ve designed, built and sold a couple houses over the years. They were all owner builder where I hired most of the work out and did some of the easy stuff myself. I currently have my latest house for sale, it’s a clean lines, modern style house on the big island of Hawaii. It’s been taking a while to sell but recently I got a call from someone who really likes it but it’s in the wrong area. Turns out the guy is very wealthy and wants to hire me to build him a roughly 6,000 square foot house in Maui with a 2 million dollar budget. He wants me to design and be a part of the building process from start to finish but I don’t know what to charge for my services. Any advice would be appreciated, thanks!