The goal of the research was to investigate the retention capacity of six green roof models (SHP1, SHP2, SHP3, SH, S, and SP) constructed with use of plastic garden trays, drainage elements Floradrain FD 25, filter sheets SF, and the extensive substrate. Models SHP1 and SHP2 were constructed in March 2017, models SHP3 and SH – in November 2017, and models S and SP – in April 2018. Models SHP1, SHP2, SHP3, and SP contained the plants (the goldmoss stonecrop). The substrates of Models SHP1, SHP2, SHP3, and SH contained the hydrogel amendment. The investigations were conducted with use of simulated (and partially natural) precipitations. The water retention capacity of each green roof model was established based on the difference between rain volume and the volume of runoff from model. The results show that green roofs can be useful stormwater management tools. The calculated stormwater retention rates ranged from 29.50 % to 85.15%. In most cases the best water retention capacity had model SHP3, constructed in November 2017 and planted in April 2018, containing substrate amended with superabsorbent (cross-linked potassium polyacrylate). The similarly constructed models SHP1 and SHP2, which were built in March 2017, in some cases have lower water retention capacity. These models contained older hydrogel and were overgrown with older, smaller, and worse looking plants, partially supplanted by mosses. Such results indicate that the efficiency of hydrogel may decrease over time. In many cases the models S (not vegetated, without hydrogel), SH (not vegetated, with substrate containing hydrogel), and SP (vegetated, without hydrogel) had slightly lower water retention capacity. The results of investigations indicate that there was a relatively strong positive linear correlation between retention depth and duration of antecedent period elapsed since preceding total (or substantial) saturation of green roofs (labelled in the paper as period since total saturation - PSTS). The weather conditions i.e. air temperature and relative permeability as well as PSTS are very important parameters that influence the retention capacity of green roof models. Result show that duration of PSTS can be stronger correlated with retention depth than antecedent dry period (ADP) elapsed since the end of last precipitation, regardless of its depth.