Building a WP site alongside an existing non-WP site

Heya guys,

A friend wants me to revamp their site but I don’t want to take their existing site down. I found some other threads suggesting to build the site in a subdirectory and then move it, but I’m not 100% confident following the instructions for moving a subdirectory.

I had the idea that after I finished the new site, I could use the forwarding option with my domain registrar to just forward all visitors to http://www.myfriendssite.com to http://www.myfriendssite.com/WPdirectory

And then I’d delete the old site via FTP.

Obviously it isn’t as clean as doing it the other way, but is there anthing that wouldn’t work here?

Thanks
Gerald