Concrete makes an excellent material for use a base for your shed, however, you will probably need to call in a professional to pour and form it. When properly poured, concrete will provide you with a perfectly flat surface to anchor your shed to. In fact, you can have bolts installed into the concrete as it is being poured that you can use to anchor your shed.
In the extreme cold, the plastic can contract which will leave gaps for any snow or water to get in the shed too. Manufacturers are getting better with this, although some reviewers are still having issues.

Let us know what you're using your California Custom Shed for, so we can help you create a shed to fit your needs. Our customers have used our buildings for more than just your ordinary backyard garden storage shed. Many have customized our storage sheds for potting sheds, tack rooms, hobby & train rooms. Some have used our buildings for motorcycles, golf carts, or riding lawn mowers. (One customer even parked a 1956 Cadillac in one of our sheds!) Others have used our sheds for a paint studio, guard shacks, offices, a dry shelter for a favorite pet, firewood storage, well pump house, or a ticket booth. Whatever your needs may be, visit us at our display lot located between Salinas and Prunedale on HWY. 101 (El Camino Real North) & Ralph Lane, and we will be happy to help you customize a building to fullfill your needs. We have over 30 buildings on display, which will show you the quality of our storage sheds, and give you many ideas you can apply towards your own building.
A successful DIY shed starts with choosing the right shed plans. First, determine how much space you can commit to an outbuilding, and check local codes for setbacks as you decide where to put it. It’s also important to consider what you’d like to store in the shed. Small tools can be hung on walls to save space, but large items like lawnmowers and snow blowers need more square footage.