foundation for a patio

[russellfl]

Hi, can anyone help?

I have recently had french doors put into my main bedroom at the back of my bungalow and want to create a patio area to walk out on. The ground slopes away about 18" from the bungalow wall and the ground level at the furthest point away be would be about 2'6" below the DPC. I was thinking of building a thermalite block wall to DPC level with steps down from the bedroom floor.
Would a single block wall be strong enough to support a hardcore/concrete base? and what depth of foundations would I need? also would i need any drainage holes in the block walls? I also have a couple of air bricks below DPC which i would have to accommodate.

Any info would gratefully received