There are currently only 3 roles at the moment...Melee, Gunner, and Bomber. So you can either...do massive damage with high risk of getting hurt, do minor damage from a safe distance, or set up hazard zones while constantly dodging. I'd like to see roles for defence, or healing.
By being an Engineer you would wield tools...wrench, med pack, sprayer, etc. Similar to the bomb, you have to fully charge the tool to use it's primary ability. You can also do normal swing attacks to deal small amounts of damage. The tools can have different uses such as...constructing a turret, healing allies within a given area, curing status effects, etc.
These are just a few ideas to get started. If you have any you wish to add please do so.
Wrench- Constructing Turrets
After fully charging the wrench you can begin constructing a turret. It takes some time to make the turret and if you get hit it will disrupt the process. The turrets can be controlled by any knight, they can vary from rapid fire with weak ammo, to slow fire with powerful ammo. Turrets will only last a given amount of time depending on their tier, or if they're destroyed by an enemy.
Med Pack- Healing
After fully charging the med pack you will be able to heal allies and yourself within a certain range that depends on the tier of the tool. The med pack takes longer to charge than any other weapon. You will also be left vulnerable for a short while after using the med pack.
Sprayer- Curing Status Effects
The sprayer has to be charged just like former mentioned. Think of a gun that sprays a mist that you aim at your allies. You'll be able to walk around a few seconds while spraying after you activate the charge. These can cure status effects depending on which one you have. Example: one sprayer cures poison and sleep, while another cures curse and shock, one for freeze and stun, and then one that has a slightly more powerful melee attack but can only cure fire.
Engineer Armor
The armor would be lightweight armor, it has lower defence but can have bonuses like increased speed.
Engineer Shield
While the shields only have average defence they make up for the armor cause they can last for a very long time before breaking. This way an engineer can help play defence for their allies. Perhaps engineer shields can deflect ammo back at the enemy as well.
Just because someone had to: Spy's a zappin ma sentry!
On a more serious note OOO said that they weren't going to do player run healing kits. This also seems overpowered, imagine four engineers in a n arena, all set up turrets and never get hit. The shield also seems to be just like the plate shields. Overall I think that there are better classes that can be made.