Website inside a website?

I want to create a website that allows people create their own website or page.But I wanna do this in different way.I don't want people to use templates,I want people to use their own html,css,php or js code.They put their codes in my website and then they create a new website or page : myWeb/peopleWeb. Can it be harmful to my website using codes instead of templates ? And how is this idea(please explain why bad or why good) ?