A Gannt Chart, in a nutshell, seems to be just what you planned on making/spending, vs. what you actually did, so you don't really need a Gannt Chart specifically. So to modify that to suit YOUR needs, you probably want to figure out how much your expenses will be, such as buying products, paying employess, advertisements and property taxes and such. Then calculate how much business you plan on having, and the income you expect to be making from that business. Also, if you are just starting a business, how much it takes to start up, if you are going to have investors, and how much you'll make at the start of a business is important. Just compare all of theses statistics, and see how well your finances are going.
Please let me help you with this. After many failed attempts at doing business, I've learned some things. I'd be happy to tell you what I know. Just ask. I do this for free, I just like to inform people, and help. Let me know if you're interested in learning anything.