This is a brilliant example/template you can use for a Design Document (dd). It’s a fantastic example and its downloadable as  a word doc.

http://www.jeanpaulva.com/index.php/2011/11/29/low-level-design-document/

Again – in many cases for dd’s this may even to bigger a document (10 pages) than you need, but its certainly similar to a few I have created for a project that is more like 1-4 weeks of work.

Great to see the database design here, because again remember that you want to get feedback for this (particularly from DBA’s, Architects etc…) and getting advice on the DB early is extremely important (DB changes are not always easy).