Engineer (Highlander)
In Highlander, the Engineer is in charge of locking down areas for his team and making sure all his teammates are getting to the fight as quickly as possible with as much health and ammo as possible. Using (mini)sentries, he can prevent the other team from utilizing entire regions of a map or force them to waste time attacking him while his team retaliates. Using teleporters and dispensers, he can support his team and keep them fighting until the enemy is defeated.
On Offense
In most cases, offensive engineering requires use of the Gunslinger. The Engineer on offense is responsible for keeping the team's flank clear and for making sure his fellow teammates on the flank are healthy and stocked with ammo. Efficient and frequent use of sentries and dispensers is vital for preventing an enemy Soldier or Scout from getting behind the team and causing havoc. The best Engineers pair proper building management with strong deathmatch skill to fortify any area they enter with their teammates and make sure that once ground is won, it is not lost. During payload offense, one of the Engineer's primary goals is to push the payload cart. Most teams designate their Engineer and their Scout to cart pushing, maximising push time at x3. Engineer's should try to keep teleporter's up as well, as the walk from respawn to the cart can sometimes be very long. Engineer's should also try to keep minisentries down at all times to increase damage output or to cover a flank.
On Defense
There are few better defensive powerhouses than a Level 3 sentry in a strong position. Positioning, timing, and build order are important concepts for an engineer to understand on defense. Building too far forward or waiting too long can cost the team the relevant control point or even the whole round. It is the Engineer's job to tank damage from ubered Heavies and Demos so that his Medic doesn't need to pop early or fall under the pressure of nine attacking players. Kills are less important to an Engineer than merely surviving because most of the other team can't come within range of his sentry as long as it is active, and going down with his sentry can be costly if a domino effect leads to multiple captures before he can build again. The team leans on its Engineer to provide a safe fallback zone when they get lit and the other team is pushing forward.
Rollouts
Stopwatch gamemodes (Attack/Defend and Payload) give the defending players a setup time to get in position and prepare for the attack. This time is primarily utilized by the Engineer to build as many buildings as possible in the first position that needs to be defended. It varies from map to map, but in general the Engineer follows a basic rollout. First, he builds a teleporter entrance just outside spawn. Then, he runs to his first sentry position, grabs any ammo pack nearby, and builds a dispenser (it is important to have the building first to ensure a ready and constant stream of metal once the round starts. At this point it is common for teammates of the Engineer (usually a Pyro, Scout, and/or Soldier) to kill themselves near the Engineer. This allows him to pick up the metal from their dropped weapons to speed up the process of building. This metal is used immediately to build and begin upgrading the sentry. Once the sentry is at level 3, any remaining setup time is usually devoted to upgrading the dispenser and building a teleporter exit if there's time. Most standard maps allow for a "complete" rollout that results in a level 1 teleporter, a level 3 sentry, and a level 3 dispenser before time runs out. In some stopwatch maps, the BLU team gets a tiny niche where buildings are buildable inside spawn (ex. pl_badwater). Engineers on BLU can use setup time to build their own level 3 sentries, allowing for interesting tactics that usually involve sneaking the sentry into a position of ambush to kill retreating RED combo members.
