Dear Gardeners

I have a lawn that slopes down to a patio at the end of the garden
covered in paving slabs. The patio is nearly 3 feet from the ground at
the end of the garden. I want to remove the slabs and make this into a
raised bed but I don't know what I have to fill it with or how much. I
presume it doesn't all want to be top soil. The two sides and the back
of the patio are brick wall while the front rests egainst the lawn.
The area gets quite a lot of sun but may be quite wet as the soil in
the rest of the garden is pretty heavy and the garden slopes that way.
The area is roughly 10 feet long and 6 feet wide.

Any advice or suggestions would be useful.