Start the chart from a high-level view first. Will you need to hire developers or do you have as many as you need already? Are you already funded or will you need to raise more capital?
Will this be a professional business? If so, you might consider hiring experienced executives and someone that understands finances well. If your site revolves around a patentable idea, you should consider what the patent process might take in terms of time and money. When would you want to start such a process?
Can you make a rough estimate of how long the development process would take from start to finish? If not, find a friend who can, look it up, or estimate. You probably want to break down the process into stages. Are there any specific parts of the development process that should be broken down?
After you know what tasks you'll need to perform and how long each one will probably take, you'll need to consider which ones need to come first. You will probably need some money before you can pay developers or executives. Are there any tasks that can be performed concurrently? Do any tasks depend on the completion or partial-completion of other tasks
You should also think about what time frame you will fit within the chart. The entire life of this venture will most likely not fit within one chart.