Friend of mine is quite large - walks around at roughly 320#, makes
weight at 308# for powerlifting comps.
He said, when he saw me doing this, Hey, I can do that, and proceeded to
freemount, ride smoothly, hop down a fairly steep curb-
Taco my wheel, break my left crank.
He owes me one. He says that as long as he’s buying me new parts, maybe
he’ll get one for himself, too; or maybe buy me a new one sturdy enough
for him to borrow once in a while.
So what should he get?
have him buy you a Torker DX. it’s a fairly priced unicycle with strong ehougn cranks and wheel to last him through that drop… I think.
Tell him if he wants to ride it he has to run and catch you riding it. And give yourself a good 200yd headstart, so he’ll have to run and lose wight before he can ride.
if he wants one for himself, a profile hub is probably manditory at that weight.
If he plans to do a lot of curbs or hopping, definitely a splined axle. He’s strong, so weight should not be an issue. Get a burly one.
I’d say at that size, if he wants one, he can take whatever he wants.
BWAHAHAHAHAHAHAH!! 
funny stuff
You might also go for an all steel 2004 model KH24. The 2005 models are aluminum, meaning they’re lighter, but don’t handle bending nearly as well. If your friend bends a steel uni without damaging the wheel, he can just bend it back into the right shape.
You could also build a custom strong and large unicycle, something like a Surly Large Marge rim in 26 or 24 inch, and a custom frame, maybe even one of the titanium frames if you’re rich enough. If you go that route I’d suggest DT Swiss spokes, they seem to be the strongest, and a Profile hub and cranks.
On the other hand, the 2005 aluminum KH models might be okay for 145 kilos.