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.
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