It's that inside knowledge which could help the 32-year-old earn a top place at an event that features on the Freeride Mountain Bike World Tour.
"Maybe it could help a little bit because I will build the course and spend a lot of time there and I'll be testing all the features myself," McGarry explains.
"But I just want to build the best course to have the best possible show. The riders come from all around the world so I just want it to be as good as it can be for everyone, so I definitely don't tailor it to my own taste.
"The level of riding on the slope style scene is just crazy, man. There are young guys coming through who are really pushing the limits and putting on an amazing show with big tricks and big gaps and trick combinations, doubling tricks up like double backflips and 360-backflips. The level is as high as it has ever been."
McGarry, together with his Queenstown-based building partner Tom Hey and a couple of others, will begin building the course in late January, moulding their vision into the lower inclines of Mt Ngongataha.
"Slope style tracks are man-made," he explains. "You build the wooden ramps and pile the dirt up with the digger and make the course all man-made.
"We are going to be building some big structures, with big trees and timber to make these big platforms that riders will jump on and off, and some big ramps."
McGarry's two-wheeled journey began as a youngster riding BMX before a growth spurt in his early teens - he now stands 1.95m - saw him shift his towering frame to the larger mountainbikes.
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He joined the slope style professional ranks in 2006 when he travelled to Canada's Whistler Park and entered the Crankworx qualification round, which at that stage was an open event.
"I entered in 2006 and made the final and I was stoked," he says. "I got 18th and that was my first ever slope style because there was none in New Zealand."
The industry took notice and sponsors gradually came on board.
The sport has since boomed, with the biggest events attracting crowds of around 50,000 spectators and the riding standard is now so high competitions are closed to the average weekend warrior.
Jaw-dropping GoPro footage of McGarry landing a backflip across a 22m-wide canyon in Utah has attracted nearly 23 million views, and rams home the controlled recklessness of the sport.
Mental strength is a huge component of slope style riding and, no matter what skill level or physical prowess a rider may possess, McGarry says the top two inches can determine whether you succeed or fail.
"It's a big battle, the mental side of the sport, just staying on top of your nerves so you can perform. It takes a few deep breaths to really get on top of it.
"You have to plan it all out and, if you have one move on your mind, it makes a difference to you on your run if you are worried about it.
"When I did that huge flip I was thinking about that, 'here it comes, here it comes', but you have to try to remain composed.
"It's a big part of the sport because you can have all these crazy tricks but if you can't get on top of your nerves and nail the run from top to bottom and get everything perfect, then you're not going to do very well. Controlling your brain is a big part of it."
Injuries are the obvious downside but are considered "part and parcel" of riding and the dry-humoured McGarry has had his share of painful setbacks.
"The stuff we do, it's not playing golf. I broke my femur and ankle, and my collarbone twice. But thankfully, what I have going for me is I haven't really hurt any of my joints. I've been lucky enough to stay intact as far as that goes.
"You've got to accept that it's going to happen and try to limit it as much as you can. I try to go to the gym a couple of times a week and stay as strong as possible so I can take a beating when it does go wrong.
"I practise tricks in the foam pits and with the air bags and just make sure I've still got the muscle memory of how fast to spin it ... so you don't land directly on your head."
With the tremendous risk comes the lure of considerable rewards and slope style riding has been kind to McGarry and provided him with a lifestyle he describes as "a dream come true".
"I can make a living from riding bikes, which is amazing and every mountainbiker's dream. I know it is not going to last forever, so I'm making the most of it."
