Greenhouses, Sheds and Sun Rooms - Building and Anchoring shed

I have a 12x12 concrete slab (w/ exposed aggregate finish), I am planning to build a 8x8 or 10x8 wooden shed on it. This will be my first attempt at a project like this, but I want to build it myself (with family help) for the experience. 3 questions:

1) I wanted to build it from a plan, but after reading a lot of threads here I'm starting to think it might be better to build from a kit (like HD or Lowes sells) since it's a first attempt, and the kit doesn't seem to be much more expensive. Does this sound about right?

2) I want to anchor the shed to the slab, and would like to be able to just use the slab as the floor. Can I just anchor the bottom wall plates to the slab, and dispense with the joists and floor frame altogether?

3) Is it better to raise the shed up and provide some air flow between the shed and the slab for drying out etc. to prevent rot or protect from seepage under the wall?

Thanks for your time (hope you don't mind if I follow up with any other Q's that occur as I plan this out),
Thanks,
Robert M

1. The nice feature of a kit, is its completeness. I modified a HD kit to build my 24x28 shop. It included everything except for the insulation and the doors.

2. Concrete is commonly used as the floor in houses and garages and such. It should do fine for your application. Just drill and install expansion bolts to hold the bottom of the walls to the slab.

3. It is better to control water by keeping it away from the building than it is to manage the water after it has intruded into the space. The bottom piece of the wall, the sole plate, should be pressure treated wood to guard against rot.

Hope this helps.

A shed is so simple that I wouldn't bother with a kit. From what I've seen they are overpriced.

I would attach PT sill plates directly to the slab. You can set anchor bolts in the concrete before it dries or you can use RedHeads to attach the sills to the slab. No joists or floor framing needed.

In my area a shed on a slab is considered a permanent outbuilding, requires a permit and is taxed as a permanent building. A shed on blocks or bolted to buried posts is considered temporary storage, requires no permit and is not included in property assessment. Go figure.

I would also build the shed the full size of the slab. The main reason for this is to prevent standing water on the remaining slab from entering under the bottom plates. Screw (tapcon) the pressure treated plates to the perimeter of the slab, build corner block studs for the corners, and fill in with studs 16" on center, allowing for windows and door openings. Control the water around it by either digging a trench and embedding perf pipe and gravel to take the water away from it and you should have a good building to work in. Supply at least a 1' overhang with your roofline in order to keep water from splashing up on the exterior of the building. Gutters are nice, but not necessary.