Any experience of installing SUDS (sustainable urban drainage system -
look it up at pavingexpert)? In particular, doing it on the cheap.

I'm dealing with about 50m^2(plan) of roof, splitting two ways, which
I reckon as two units of about 1/2 m^3 of soakaway each. Space is
somewhat limited, so I want a high void ratio soakaway: one built from
plastic cages, rather than a hole filled with rocks. As it's low
traffic, low budget, I'm thinking about subbing a 300 quid commercial
plastic crate with a stack of inverted beer / milk crates.

Any thoughts?

Any favoured brands? 8-)