OK, here's another good site: https://uwarboretum.org/eps/research_act_classroom/rain_garden_curriculum/Resources_and_Vocabulary/Rain_Garden_Resources.pdf
it has links to several different sites, some perhaps closer to you, some with detailed steps to installing a rain garden, etc.
Aannndd, one more: https://www.news.wisc.edu/13823 That last one is an article published in the college newsletter last year. Very interesting, it purports that the type of construction matters more than the plants inside. In a nutshell, their very preliminary study seems to point to the fact that there is a perimeter berm to contain the water helps the water to percolate rather than what type of plants the garden contains.
this is a brochure I picked up from that lecture. That's it. I think. Maybe.