I also prefer a concrete slab. I'd put in a 3" slab. Since the shed's so small and it doesn't get real cold in RI that should be thick enough. Be sure to use rerod at the recommended intervals. I'd rent a cement mixer. It'll take forever to handmix an 8'x 12' slab. It'll take a while even with a rented cement mixer. Be sure to put anchor bolts in the slab after its poured, so that you can place the sole plate over the anchor bolts and bolt it down.
That said, here's a good alternative. I used it for my 12' x 24' shed and like it. Use a pole barn style of construction. The basics follow. You sink pressure-treated posts that are 6" in diameter 24" into the ground. They should be pressure-treated to keep the underground part from rotting. The recommended distance between poles is 8'. For your shed you'd put a pole at each corner and one in the middle of each 12' wall. Make SURE the poles are plumb and that on each wall the outsides of the poles line up perfectly, and that the top of each pole is cut so that the top is level AND is level with the top of each other pole. And of course make sure the poles form a perfect rectangle. If your brother's carpenter friend knows anything about framing in buildings he can tell you why all that is necessary. Its the most important part of the building process for a pole barn style building. Then, starting 3-4" above ground level you nail or screw on 2x6's horizontally over the outside of the poles about every 2 1/2 ft. on center. It'll take 4 rows. The bottom of the bottom row should be 2-3" above ground. The top of the top row should be even with the tops of the poles. A top plate goes on top. It consists of a 2x6 laid flat on top of the poles and the top row of horizontal 2x6's. The outside edge of the top plate should line up with the outside face of the top row of 2x6's. Two poles are used as a support to which to attach the door framing. You can use a corner pole or one of the poles in the middle of the 12' walls for this purpose and will only have to install one extra pole for the other side of the door.
Of course you'll have leveled the building site. You can leave the floor as dirt or cover it with small rounded stones -- 3" of stones would be enough. If you cover with stones, raise up the bottom layer of the outside row of horizontal 2x6's by the inches of stones to be laid down. In other words, if you lay down 3" of stones, the bottom layer of 2x6's should be 2-3" above the top of the layer of stones. The best time to lay down the stones is after the poles are in and before installing the horizontal rows of 2x6's. I won't go into why -- trust me on this. It has to do with ease of building the rest of the shed and ease of laying down the stones.
The nature of the outside framing (the horizontal 2x6's) will of course determine, and limit, the types of siding you can use. The roof options are the same as for a stick built frame, and the options for framing for the roof are the same, and the framing goes on just like it goes on a regular stick built frame.
To help keep out mice, and to help keep rain water and runoff from getting at the floor, I put the door on the downhill side of the shed. Then, all around the outside of the bottom row of horizontal 2x6's, before putting on the siding, I dug a slit trench. I fastened the top edge of 12" wide aluminum sheeting to the outside face of the bottom part of the bottom row of 2x6's. The rest of the sheeting goes in the slit trench, which of course you then fill up with dirt. The siding covers the part of the sheeting that's attached to the bottom row of 2x6's. If you do this and cover the floor with stones, pour on the stones AFTER you install the aluminium rain/mouse guard sheeting. I built my shed myself 13 years ago and used this rain/mouse guard sheeting technique (which I'd never heard or read about and thought up myself). I've never had a wet floor (I have 3" of stone on the floor). I do have mice, but its all but impossible to build a mouseproof shed, and that's what D-Con is for.
No way a hurricane is going to blow down a structure like this. I don't mind the stone floor at all.
