Buy v Build study on programming for site

I know what I want the site to do (from a user and business perspective), and would like a programmer/web developer to take the functions and features, and advise on the best way to build the site, including looking at a straight programming, using and modifying open source, or subscribing to already built functionality.

This should be a one day job of research of what's available for each function, and advise what is best to use to build the site.