Before starting your project, you need to prepare your area where you will be laying the patio. Make sure to dig the area up if you're laying paving slabs that are already in place. Dig a depth of around 150mm across the whole area, and ensure your soil is even and flat. Then tip in the sub-base, raking it into a consistent depth of 100mm, ensuring the cement is flat. Prepare a concrete mix of one part cement, 3 parts water, adding water to create a a thicker consistency. You can use a cement mixer, or a large tub or bucket.