How important is the floor base? Is it mandatory to have before the shed is placed?

No, it is not mandatory. It does help with the sturdiness of the unit.

How do you attach shed to the wooden platform?

You usually bolt the bottom frame using screws you would get from your local hardware store.

Can I purchase an 11 x 13.5 Lifetime shed in a color other than tan/brown?

Those are the only colors available.

Are there guidelines for preparing the ground on which the shed floor will lie?

We do not have specific guidelines for the ground, but the manufacture recommends it be installed on wood or concrete platform.

Where are lifetime sheds manufactured?

The Lifetime Sheds are manufactured in the US and have their own plastics factory.

What is the warranty on the sheds?

Most sheds come with a limited 1-year warranty but it also depends on the particular shed.

How long will it take to set up? What size pad is recommended?

Set up time differs depending on your level of experience with assembling this type of product. The concrete pad should be approximately 4". The actual dimensions of the shed is 96" x 150". Since the floor dimensions are a little smaller, you would need to build the floor at 93.5" x 148".

When is a cement pad needed for construction?

Whether to erect Lifetime sheds on a concrete or wood-constructed platform is completely up to your own discretion. Lifetime does recommend a concrete platform for maximum durability. You may also want to check with your local building authority for any other requirements.