Call of Duty

Mission: Highrise

This will (kinda) require 2 runs in order to get.

Run 1: Earn the Ascender
The first time you play this mission, you'll want to follow the arrows until you earn the ascender, which is a rappel tool allowing you to go up ropes. Once you have it, restart the mission.

Run 2: 45 seconds to the roof
With the ascender picked, it'll automatically spawn in your inventory the next time your start this mission. Once you spawn, equip your pistol as you'll run significantly faster. You can now immediately ascend up two ropes, jump out the window to a zipline and easily get to the roof in 30-40 seconds.

Mission: Highrise

You won't be able to complete a rooftop run in under 45 seconds, until you've found the ascender tool within Highrise for us to fly up the yellow ropes. So the first part of this guide will show you where to collect the ascender tool before attempting a speed run!

Ascender Tool
First of all we need to reach floor 10, where the ascender tool is located. The general rule of thumb here is to continually move upwards, may that be via a ladder or staircase. My personal preference was to constantly turn right when the paths split. So for example as you come out of the first elevator shaft turn right, collect the night vision goggles and navigate your way through the dark room, head up the staircase, right out the window, follow the gangway all the way to the end, enter the window, hang right to climb up another elevator shaft, right three times and go up a yellow ladder, go out the window, follow the yellow tarp, take a right and follow the corridor to the very end to find the tool in a orange box.

45 Second Run
Once you have the ascender tool, restart the mission and attempt a speed run. At the first elevator shaft, ascend , take your left and dispose of the two enemies in the corridor. At the next staircase ascend , take a left and zipline out the window. Then follow the scaffolding around the outside the building before ziplining one last time towards Price.

MW3 - Elevator Out of Order
Reach the roof in 'Highrise' under 45 seconds

Mission Highrise

This will require 2 attempts in order to get, if you do not already have the Ascender.

First run: Earn the Ascender
The first time you play this mission, you'll want to follow the arrows until you earn the ascender which is a rappel tool allowing you to go up ropes. Once you have it restart the mission.

Second run: 45 seconds to the roof
With the ascender picked up, it'll automatically spawn in your inventory the next time your start this mission. Once you spawn equip your pistol (I used a shotgun) as you can run faster. You can now immediately ascend up two ropes, jump out the window to a zip line and easily get to the roof in under 40 seconds. Fallow my video for the exact path.

First you need to acquire the rappel tool which can be found by a stairwell (the north west i believe). After you have done this and can replay the mission*, head up the initial elevator and continue until you see 2 guards down a hallway. Take them out and proceed to the far end where you can rappel up a stairwell. Look left as you exit for a zipline and follow the edge of the building until you reach another zipline. Here you will meet Price. If you complete all that in 45 seconds you will get the achievement.

*Andrew RNG notes that you can collect the rappel and immediatly reset to get this done faster

Play through the mission "Highrise" in MW3 as normal until you gain the ascender.

Reset the mission or jump out the nearest window.

From the mission start, make your way to the elevator and use the zip to go up. Take the first left, take your pistol out, take out the 2 enemies, and at the end of the hall, turn left and use that zipline to go up more floors.

From that floor, turn left and use the zip that takes you out of the window. Follow the scaffolding until you reach another zip line, take it, and climb up the ladder and if you do it all under 45 seconds, the achievement should pop!