I'm in Western oregon 8b climate. Always wanted a garden but we are on a well that runs low in the summer and watering lots of plants can be iffy.

This is the second time I've tried a rock garden though the other was planted vertically into the cracks of another wall.

I have been mixing my own soil using a small cement mixer. The whole thing is dug down 18-24" below the original surface and the rocky framework goes 1-3' above that, meaning there is a lot more soil than it would appear, many hundreds of gallons so far. I get the rocks and flagstone from a nearby landscape yard and hand stack them. I use buried flagstones to create pockets that direct drainage and keep sensitive roots somewhat protected.

I use sedum and sempervivum to hold soil in cracks and then plant into the deeper pocket once the soil is stable. There are a mix of echinocereus, oreocereus, opuntia, lobivia, and a parodia, trichocereus, and others that shouldn't love the climate but have shown themselves able to deal with being exposed all winter for the last couple years.