Measure along all walls corner to corner
Measure from corner to outside edge of the door casing. Measure door from outside trim to outside trim (if there is trim on the door)
Measure from corner to outside edge of window trim. Measure window outside of trim to outside of trim
Measure window from floor to outside of window trim. Measure the height of window from outside of trim to outside trim
Measure from the corner to the center of your sink
If you are keeping your appliances, measure the width, height and depth of all of your appliances (fridge, stove, dishwasher, microwave). Measure from the corner to the edge of each appliance to note its location on the wall. If purchasing new appliance bring the new specifications with you measurements
Measure from the corner to any outlets, switches or vents that may interfere with the cabinet design
Measure from the floor to the ceiling. If there are bulkheads measure from the floor to the bottom of the bulkhead, also the height and width of the bulkhead