Or what’s the easiest way to make one or two.
Stack pallets to the height you want. These are often given away at grocery stores or you can find them at the curb on trash day.
Make a wood box the same size or pallets
You could use two pallets wide, two pallets tall. Then face the pallets with one or two boards stained or painted to you tast. ☺️
Unless you reinforce the pallets, they will fail in the short time and vibrate tremendously. Washers and dryers need firm stable surfaces. Better to build proper pedestals or boxes for them.