I used an old 36" cocker unicycle steel rim and 20x20mm steel tube. Everything in steel. The total weight of the steel 36" UW is 8.1Kg (Steel), my normal g36 weights 8.4Kg (Aluminium, 8.1Kg on the pic is wrong). My Nimbus 19" Trial is 5.3Kg (Alu).
The heavy 36UW rides perfectly fine. Weight of the wheel is irrelevant for me as I did not notice cutting the rotating mass by the factor of 2 on my g36". The same conclusion here:
The Worlds Heaviest 36’’ Unicycle Wheel
He also notices that the rotating mass does not matter or even has many advantages while riding.