a discarded plastic tub,
and aluminium foil.
Choose a strong round tub ( about 15 cm diameter) with a tight fitting lid. Carefully remove the centre of the lid using scissors leaving the rim in one piece. Put a few stones (or thin layer of cement) in the bottom of the carton, to prevent it blowing away in a strong wind!
Place a sheet of aluminium foil over the carton (I find the cheapest narrow rolls (20 m x 200 mm) of 'saver' kitchen foil suitable), taking care not to crumple it, and fix in position using the rim of the lid. The foil should be as smooth and tight as possible.
Expose the hailometer outside in your chosen position. I have mine set up on a small plinth inside a larger plastic plant pot. It sits 5 cm below the outer rim with 2-3 cm space around.
The reason? It helps to prevent birds perching on it, perforating and fouling the surface. They perch on the flower pot rim. Examine the pad at least daily, or as often as you like but remember daily records run midnight to midnight GMT.
Hint: Small snow grains do not usually mark the pad. Snow pellets, even large ones, being of small mass make only a light impression. Ice pellets make a definite mark related to their size. Large hailstones can penetrate the pad. Make a record of the days that you detect hail. If you keep the marked foils you can compare the marks you find with previous records and build up a comprehensive record at your 'hail station'. I would be pleased to hear about any observations you make.