site under construction home page query

sorry if this has been asked before, i did a forum search first but couldn’t see it, at least i couldn’t find it. if it has been answered before i apologise but please excuse this is my first question.

i would like to start building a new site using your word press theme over the top of my old html and css driven site at http://www.ptservices.co.uk. i don’t really mind the site being down for a week or two as it doesn’t get that much traffic (even if it is ideal), but i do at least want to have a (this site is under construction) home page. i guess this is poss but when i start to add new pages in word press through your theme for my site, won’t they also show when people visit the site. is it poss to build the new pages in the background (and also be able to preview them so i can see how the site is progressing) yet only have the site is under construction page showing for those people that visit the site until the new site is ready to go?

thank you kindly,
paul