This is a drain scupper such as is used for flat roofs such as tilt ups, which are very popular here in Silicon Valley. The top of the scupper is 2' wide in HO but the part could also be used in S and O to represent smaller parts. The opening at the bottom accepts 0.040 x 0.060 styrene to represent the drain pipe.
This part was deisgned designed by my friend Jason Hill of Owl Mountain Models, you can visit his store at owlmtmodels