Changing WordPress Theme – Start fresh or modify existing site?

Hey there,

Have a guy who wants me to redo his existing WordPress site. He found a theme that’s quite different than his existing theme, with a completely different layout. Should I just install the new theme and change the theme of his existing site and just tell him it will be under development for a few days while I rearrange his existing content…. OR, do I create the new site from scratch on a demo site with the new theme, develop completely and then do the switch over of deleting his old site and migrating the new site from my server to his?

Just looking for some advice to make the process as painless as possible. Maybe there’s a way to work on his existing site with the new theme without disrupting his existing site in the meantime?

Cheers.