A site is no different than other businesses. A great deal about it being successful is the amount of effort you put into it.

It sounds like you aren't really getting what you want. Sure you have the domain but if it just leads to his site than your not really doing a site of your own. If you have ideas than give them a try. If you want to start out getting some experience than start a site that is hosted and only costs $20 or so a month plus your time. If you have to start small than do so, sure you might not make a million dollars in the first year but it is a start.

Honestly I don't know why he just shot your idea down like that. Even if the idea isn't a new one, many of the most profitable companies on the planet have never had an original idea. Just because it isn't a new idea doesn't mean it can't make money.

I refer back to my earlier statement. Do what you want, if he cares he will stand by you. The worst that can possibly happen is that one idea doesn't work and you try another, you've spent a little time and a little money but you can try again. However if you never go for it than you can't possibly succeed.