There is a growing base of information on raingardens, particularly in the UK. Below are some websites, books and publications which you may find useful.
10,000 Raingardens for Scotland website.
RBC Chelsea flower show raingarden
International:
US Environmental Protection Agency
Books:
Rain Gardens: Managing Water Sustainably in the Garden and Designed Landscape; Nigel Dunnett and Andy Claydon
Creating Raingardens; Cleo Woelfle-Erskine
Planing Green Roof and Living Walls; Nigel Dunnett and Noel Kingsbury
Small Green Roofs: Low Tech options for Homeowners
Gardening Vertically: 24 Ideas for Creating Your Own Green Walls; Noémie Vialard
The Dynamic Landscale, Nigel Dunnett and James Hitchmough