Advice for garden shed

I'm planning to build a garden shed and have available a concrete slab where a round grain bin used to be.  I'm wondering if I can simply bolt sill plates directly to the concrete or should I put a row of 1/2 height blocks around the perimeter and have the sill plate raised up?  I've never seen standing water on the concrete slab in the over 12 years I've lived here and I plan to use pressure treated for that part of the construction.  The rest will be normal construction grade lumber.

Me personally...

I would use 4" x 8" x 16" solid block, this will keep any siding from prolonged exposure to rain, snow, etc.. 

I would just bolt the plates in place, but that's just me. If your climate doesn't call for extra measures and your using treated wood anyway, why go the extra mile? If it were your house, that would be one thing. but for a shed I'd just keep it simple. 

As it is just a garden shed you can go with a simple work but we can not trust on climatic conditions, work should be perfect so that in future you don't have to face problems regarding garden shed. Its much better to take advise of a professional roofer before you take any action because these guys know their stuff very well.