DallasDrain

I am not from Houston (Dallas) but know a great deal about what you are trying to resolve. Whom ever you use should not use 4" , flexible, corrugated pipe. The corrugation ribs restrict flow and allow sediment and debris from the roof or surface basins to collect within the ribs. Roots can also easily penetrate the snap together connections. Over time, these installations typically fail due to clogging and are very difficult to clear. Instead, specify that all down spouts are connected to solid, 4" smooth bore PVC pipe. It is possible to specify SDR 35 wall thickness because Schedule 40 is typically over kill for this low pressure system. The down spout connections should then drain into a solid, 6" smooth bore PVC main trunk line. Use "swept" bends at all connection points. Check your local municipal building codes to ensure that the exhaust point(s) at the curb or alley are in compliance. Typically, a curb must be cored rather than cut. A better performing drainage design will have a 1% or greater negative grade fall throughout the system. However; this is difficult to find naturally occurring on a typical Houston lot. Dallas has the same issue. Therefore; ensure that the height of the 4" connection point on the down spout is made high enough above grade to always "push" water to the exhaust point. This design takes advantage of the hydrostatic pressure available from the height of the roof. There are many other site specific design points to take into consideration but these are the basic ones. Chuck