When leveling pegs, a spirit level on a piece of straight timber can be used over short distances. Over longer distances, use a water level made from a length of clear plastic pipe filled with water as shown in the diagram on the right. Provided the pipe is carefully filled and has no air locks, the water at each end or the pipe will be exactly level. Large areas of paving should have a fall of about 1 in 40 so that water runs off adequately. Set the high side first, then the low side.
All concrete needs to have a solid base of adequate depth.
Dig out the area to twice the required depth of concrete below the finished surface level. Once dug, compact the soil in the base with a garden roller or similar, then place and compact a layer of crushed stone or hardcore, leaving sufficient space for the depth of concrete required. It is always advisable to place a layer of polythene between the stone base and the concrete prior to laying, to prevent moisture from within the mix being absorbed by the dry hardcore beneath it. Check that all levels and falls are correct, and that pegs do not project above the formwork. Measure the depth, width and length in metres and multiply these together to determine the volume of concrete in cubic metres that you need to order.