WP - Best way to active/deactive under-construction page?

Is there any plugins that allow easy on/off under-construction page? Something with a progress bar will be nice but not necessary. I have checked out some themes available on themeforest, never used them. If I do install those themes together with my main theme, does that mean I just swap them around under Apperance > themes? Not sure if that makes sense? Thanks.

Theres a plugin dude. I think it's the first one you get when you search for "Under Construction" in WP plugins. It allows you to set a custom message which could easily incorporate a progress bar if you like. And you can toggle it on and off easily.

Edit: Here's the link:
http://wordpress.org/plugins/underconstruction/

And here's a progress bar you can insert with a shortcode:
http://wordpress.org/plugins/progress-bar/