I am doing a retaining wall for a customer that surrounds half of a pool. The wall is 100 ft long with one 90 degree turn, and three foot high, total sq ft is 300 ft. I am probably going to use the medium sized interlocking block (at lowes etc for $2 a block), or should I use the bigger ones (at lowes etc for $5 a block)? I know the bigger ones are more sturdy, but are alot more expensive to use. I was planning on using small gravel (what size?) underneath the blocks, running black perferated pipe inside the first layer of block for water drainage (surrounding it with gravel as well), and lining the entire wall with dupont landscaping fabric. Any problems so far? It will take 900 medium sized blocks, and will probably cost just over $2000 for materials (block, fabric, pipe, gravel). I need help formulating a total cost for the customer. There will also be backfill needed, but no cutting, this will probably be a separate charge from the wall. Are there any formulas for this??? Should I calculate the estimate from the square footage, what are the going rates? Any help is greatly apreciated.