If you haven't completed the task yet........
How you approach this dependes on the final usage of the area.
If you just want to use it for walking on or having a seating area then about 2'' of 20mm gravel first then 3'' or 4'' of concrete.
Wait for this to set then put your tiles down, setting them with a mortar mix of sand and cement or ready mixed mortar in dry form.
If you intend to park a car as an extreme example, or have some other heavy usage of this area, then the garvel should be 4'' deep and concrete should be 4'' deep.
If you had a load of old rubble like broken bricks, then this can be used in place of the gravel which can cost Â£80 a tonne. Just level them off as best a you can.
You need to take into account the final level (2'' or 4'' gravel plus 4'' of concrete plus the thickness of the tiles or blocks on top) and may even have to dig down further.
A lot of concrete is usually needed, even for small jobs.
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