Do a website on what you like to do in life. Do you like video games? Make a video game site. Do you like to program (you know I do), then make a programming site. What are your favorite subjects or fields of study? Do a site on those. You might as well build on something you love to do because then you will look forward to adding cool things to it and growing it into something popular. After all, if you like something then other people who like the same thing will flock to it.
Word of advice is to start small. Your first site is going to look plain and simple and maybe a little ugly. Don't let this discourage you. Just build on it with a steady pace. Add little things here and there and pay close attention to detail. Just think, if you made one small change a day, in a month you will have 30 changes! Even a bad site with 30 decent changes will improve its look greatly. Now if you did two changes a day for a month, 60 changes!
Get help when you need it. Want some better graphics? Ask a friend who likes to do graphics to help. You don't have to do it alone either.
Good luck with the site.