I have chosen bing-wu as his most probable hour pillar. With this hour pillar, Bill Gates' chart is a follower chart. Both the xin resource stars are buried in the earth and there is no other self and resource star to support his ren daymaster. Remember that a follower chart is treated as a strong chart.
There are 3 reasons for his amazing great amount of wealth.
1. Bill Gates' fire wealth stars are strongly rooted.
2. Si-wu-wei is the fire seasonal combo. In his natal chart, wu-wei can pull in the si to form the fire seasonal combo with the help of the 2 bing stars in the stems acting as lure and thus, creating more fire wealth stars.
Remember that a follower chart is afraid of the resource star because it can cause the structure to break. Bill Gates is currently in his geng-chen luck pillar with his geng resource star protruding. Luckily for him, his fire stars are very strong and so the negative resource star is well under control.
Bill Gates is also a great philanthropist with a very big generous heart. In the year 2000, Bill Gates and his wife Melinda combined 3 family foundations to create the Bill and Melinda Gates Foundation. This foundation is easily the wealthiest charitable foundation in the world and it aims at eradicating poverty and providing education and healthcare. Currently, the funds are helping in more than a hundred countries. Very good karma, Bill Gates and not forgetting Warren Buffett, who has also contributed much to this noble cause.