I spent about three weeks looking for the drainage mat online, I found places in California and Ontario. Then miraculously I found a place in Burnaby that had exactly what we needed. You don't always need a drainage mat for a green roof but because our roof is quite flat (it slopes about 1.5 inches every four feet) drainage is very important.
We had top soil which we mixed in with pumice and coconut coir. We picked coconut coir since it's a by-product and renewable, unlike peat moss, and we picked pumice over perlite again for its lower environmental impact. I'd read about some even greener alternatives, such as recycled glass growstones but these don't seem to be commercially available yet, We used 1/3 of each material. I'm a little worried this mix will hold too much water since both pumice and coir are more water-retaining than their counter-parts but we'll see how it goes.
Next week we'll finish the dirt and hopefully do some planting!