Question: I live in Arizona and I'm building a raised patio 12" to maybe 18" at most in the back of the yard. The perimeter is horseshoe shaped and retaining wall blocks are embedded in concrete footing. What do I back fill with to raise the inside? Gravel? Dirt? I plan to finish the top with pavers or flag stone. This will be contained on all sides by the retaining wall. We have minimal rain or freezing. Does this still need drainage? I was thinking of lining with fabric and then backfilling with 3/4 gravel until 3-6" of the top adding sand and setting the pavers (filling between with sand/mortar mixture). Thanks for any info!!