Well, Space Guy's been working on TF2 packs of weapons and mods, and I think it's time someone should make an engineer mod.
Sentries:
You know, there's a console command of when you type it, a bot spawns where you are?
Someone could make an item that will activate that, specifically the Engineer's box, and instead of a bot it would spawn a sentry.
Dispensers:
As for the dispenser, you could make a brick and you know, events are putting little parts of scripts into events? Well it could be that the dispenser it a brick and when it gets planted, an invisible bot gets spawned inside it, with a no-model modified no ubercharge feature, so iy would heal. And you know the medigun supplies health? Well you could make this item that the bot's holding also supply a variable: Metal!
Teleporters:
As for the teleporters, you know the event "setplayertransform"? Like I said before, events are scripts but in the event language? Well, instead of the event language you just use normal script, and the teleporters could be bricks. Like tele1 and tele2.
And you could make a mod where you can only plant one :>
And when you plant one it reduces your metal ^_^
