I need a functional specification document creating for a new web business

I am in the process of creating a new Accountancy service in the UK. I have developers lined up but i need help in documenting the functional specifications to enable them to build this site. The document does not need to be detailed just break down the core elements and what needs to be constructed across the site.

I have attached a similar type document from another project that i have been involved in although this system is not build so no screen shots etc required.