Hi, read this useful and good web site http://www.sswm.info/ there are a lot of useful information and "Linking up Sustainable Sanitation, Water Management & Agriculture" as they say in the home page.
There is also a well build section on treatment wetlands:
http://www.sswm.info/category/implementation-tools/wastewater-treatment#(Semi-)Centralised Wastewater Treatments
in the hardware side there are explications about free water systems, horizontal systams, vertical systems and also hybrid systems.
Read all the articles and you will find in the bottom of the pages a good, complete and free download library about treatment wetlands!!!