There are plenty of snakes that potentially fit that description but if your asking which species are going to get that large you might want to do a little more research before picking up a "big" snake. In the initial post you stated you where looking for something 10 foot or longer and heavy bodied and then I read the 15-20 foot statement. Seeing a big snake at a zoo and working with a big snake of your own are two entirely different things. Alls I'm getting at is it might be a good idea to find someone who works with big snakes so that you can talk to them and get a better feel for what it's like to both handle and care for big snakes.
As for suggestions I didn't see anyone list the bredli carpet python (its a heavier bodied carpet). I also wanted to jump on the bcc boa suggestions but my only concern is the fact that BCC's are less forgiving of husbandry mistakes making them a more advanced keepers snake.