Creating new site using your page templates & child pages

Hi
We are looking to change the layout & look of our pages using some Highend templates & are going to start using parent & child pages.

Are we better to just build this new site as a new WP install then have it moved over to our URL or build it inside the current WP install. (we have a cloud server & use Plesk)

I have a feeling it will just be easier it start with a fresh install, but I will take your advice.

Thanks in advance
Steve
http://www.reds-removals.co.uk/