Registered user without a site

Hello,
I’m trying to change the poor looking page for the user who did not create the website during the registration (see the screen shot). My guess I need to use Ultimate Branding plugin to customize that page. No luck so far. I’m trying to figure out how I can explain to the user that he or she needs to create a site. Some sort of the user interface where the user can realize what needs to be done next. Or maybe to make mandatory to select the template during the registration I'm using Blog templates plugin, but I have no idea how to do that. I would prefer the mandatory selection, but either way will do.
Thank you