Creating an e-commerce site would be a big task. You can absolutely code the software yourself but you would have to be very savvy in the programming language that you would code with. There are plenty of e-commerce software packages out there for sale. It would take a lot of hassle off your work if you had one already made. There may also be free software packages available, just google free e-commerce software. This will definitely be a big task and will require you to not just visually make a site with wysiwyg programs but also incorporate a program into it and make the whole site functional.