There are a bunch of companies that make downspout nozzles (such as Wade Drainage), which are often used to terminate parapet rainwater outlets into hoppers etc.

We'd like to use them on our projects as rainwater overflow outlets off flat roofs/balconies, but they're generally made out of bronze or the like and cost about £150 each.

I'm looking for a cheaper option (besides the contractor sticking a hole through the wall). Any ideas?