raised bed

If you're building it from brick, block or concrete, don't forget to incorporate drainage holes near the base level.
When I built mine, I laid membrane at the bottom, covered with 1.5 ins. coarse gravel, but any hardcore will do.
I then filled it (and the purists are going to YELL at me now) with a mix of good quality topsoil and compost. That winter I incorporated some very well rotted horse manure, and in the spring topdressed with multipurpose compost. All in all, the whole thing has been very successful.
Hope this helps.

I am obviously not a purist, Bbb, as I see no reason to yell at your compost mix- I assume for veggies.

To be truthful B/holic when I built it I wasn't sure what I was going to grow in it. I simply built it on some wasted space that couldn't be cultivated. This year it's been home to roses and dahlias, with a few Argyranthemums thrown in for a bit of late colour.

You could put stones or gravel at the bottom to help the drainage but not builders rubble.