You can use belugahomes.co.uk as a reference (both for the business and for the website structure).
Single page design, featuring all content but the development details;
a) Intro/splash/mission statement/profile.
b) Overview of all current developments (see reference site). The definition of current could be developments underway but not yet for sale, developments underway and for sale, developments finished and for sale, and lastly developments finished and sold. These should be marked/differentiated as such. However it is likely that only current offerings will be shown, especially as the number of completed developments grow.
Development detail, shown by clicking on the relevant development on the homepage and the other content sliding down, featuring more details about that specific plot;
i) Description of the development. This may be structured, e.g initially it may be a paragraph, but may extend to describe different elements (description intro, local area, eco build credentials, description of different types of units available etc) so heading styling should be included.
ii) Structured photos.
iii) Plot plan.
It should be possible for both ii) or iii) to not be present and the page not look incomplete.
Both photos and the plot plan will be illustrative for the page, but the possibility (if larger versions exist) to enlarge them (via a lightbox or another content pushdown), plus perhaps download the plot plan in PDF should be accounted for.
c) Contact us.