By learning web designing on one`s own, how long till we can build our own website?

I have a website in mind i would like to try to create, since paying for it might be kind of expensive. It`ll be a mix of Fluther and Google`s Orkut. I don`t plan on it being a big site, since there really isn`t any new concepts. I just liked the idea a lot, and would like to create it. Anyways, how long would it take for me to learn html on my own, before I can create a site like that by myself?

Consider that the site would have:

A forum type thing
A membership
Member`s profile customization ( not like myspace, just – about me, and other stuff that can be written on it`s page)
Some live questions and answers section like Fluther`s.

Consider also that I know very little on Html, and would be starting from scratch. Might as well tell me in what order should I learn things, such as javascript, php, html, etc. Appreciate it! =)