Haestad Methods is coming out with a book on Stormwater Management (sorry, can't recall the exact title, but check their website).  They are currently taking "pre-orders", but when I corresponded with one of their people a few months back they said it was going to be ready to ship in August/September.  I have their Water Distribution Modelling and Management text and have found it very informative on both theoretically and practical matters.  I expect the stormwater text will be just as good.

If you work for an engineering firm, know someone who does, you might benefit from studing copies of actual stormwater design reports/briefs.

Considering that the areas to be provided with drainage system are likely to be relatively small, computation of runoff will involve identifying contributory area, rainfall intensity and impervousness of the draining surface, if Rational Formula is to be used. Water and Wastewater Engineering by Fair & Geyer will give the requisite method. Hydrology and Water Resources Engineering by Santosh Kumar Garg is another book that may be of use. There used to be a UNESCO Manual in 2 Volumes on Planning and Design of Drainage Systems which if located will be a good guide. Other than that if Reports on similar works carried out by consultanacy firms or educational institutions can help as better guides to follow.

I picked up a really good reference from Half.com for less than $20!!!

Stormwater Collection Systems Design Handbook, 2001 Larry Mays

I've been designing drainage systems for years and am impressed that this book brings together so many different topics, and provides enough depth to apply the information.

Also recommend Stormwater Management, Martin P. Wanielista and
Hydrology, Water Quantity and Quality Control by Wanielista, Kersten and Eaglin. The latter comes with software called SMADA which includes many useful utility programs and hydrograph calculation.  Both excellent books.

Good luck.

remembering that most of your designs will be submitted to and must be approved by public agencies, obtain the policies and standards from the agencies you would be submitting to.  Each one will likely have different methods for doing the same thing. For examples of this, see the following links:

city of phoenix policies and standards
ftp://www.ci.phoenix.az.us/pub/payf/swpolicy.pdf

County hydrology manual
http://www.fcd.maricopa.gov/Resources/DL/Hydrology%20Design%20Manual.pdf

county hydraulics manual
http://www.fcd.maricopa.gov/Resources/DL/FCDMC%20Draft%20Hydraulics%20Manual%20-%20November%202002.pdf

Dewberry and Davis make a great book for all aspects of site development.  It is expensive but well worth it.  Cant remember the name of it but it is something like "Land Development Guide"