Container garden and any excess when it rains. I'm wanting to build a garden space that sits above drainfield. It will need to have its water diverted away from drainfield area. That's where tar paper would have come in. I would have placed it on the 3 foot paths between the septic lines. There is a natural slope in the yard and I will use that to bring water to opposite side of yard and create a catchment area- maybe, or use it, the water, in some other way.

Because our old metal shed is losing its roof to rust and contained our garden amendments we decided to build a new wooden garden shed. We purchased a Costco kit (Costco is a members warehouse store with an online component as well as physical stores). They were having a sale on the 10ft by 8ft kit shed for $799 which would be drop shipped to our house. We began by preparing a spot next to our vegetable garden area. The site selected is not flat and that led to some complications, but our property slopes throughout its length so this section was really no different than anywhere else. We used pier blocks for the base with pressure treated 4x4's. We used closer spacing of the floor joists than was required. We laid the dance floor down (it became the main construction place.) The first wall was put up. Then the side walls were put together. Front wall pieces and first shelf put in. Roof joists were put up. Roof panels were screwed in. After the tar paper, the roof shingles were nailed in place. Doors were hung. A deck by the front door was constructed, and stairs done as well. Caulking of vents, solar panel for light was placed, and tools were hung up. Success was declared. The entire process working mostly on weekends took almost two months for two people who are amateurs in the building world. It is satisfying to have built it ourselves, and probably cost in the $1500 range when all was said and done.

I don't have bees anymore, but I still help out a friend with about 15-20 hives. My hive stands were concrete/cinder blocks too. But, on top of the blocks I had some 3X3 foot (approx) fiberglass tops. These had been used to cover pallet box-sized lugs for curing hams. The tops were white with a small moat-like depression to keep it rigid. They also had the advantage of blocking any weeds from growing too close to the hive. On one site, because of the incline on the side of the hives (I almost always had mine facing east), I had an old step ladder dug into the hill with 2 short 2X6 treated. From left to right, with the incline on the right, one would see the alum. step ladder, the 2X6 and the hill. One hive was waist high, the other about knee high from the ground. Although it sounds workable, working on a slope was quite unhandy. I too tried several configurations before settling on the cinder blocks and the fiberglass tops. Inelegant, perhaps. Ease of set up on flat ground, wonderful.

Don't use felt between the layers. My personal preference is to use BC underlayment grade plywood instead of CDX sheathing grade plywood.