Start by putting the corner cabinet in position. Use your spirit level, from corner to corner, and set the adjustable feet on the cabinet to make it level. Now place the oven cabinet next to the first. Make sure the two cabinets are level with each other, use the feet on the second cabinet to line them up. Bring in the end cabinet and do the same. If you have drawers on your end cabinet, allow for a 20mm setback so that all the cabinets remain flush.