DISCLAIMER: I might take a couple ideas from other commenters to give their idea more limelight to the developer.
Name: Consuction PDA
SENTRY
Stat 1(Positive): Can Stick to walls and ceilings.
Stat 2(Posotive): Sappers have a low chance of "Falling off" and are deleted.
Stat 3(Positive): Makes Less noise than regular sentry.
Stat 4(Negative): Costs all 200 metal.
Stat 5(Negative): Can only be upgraded to level 2.
Level 1 sentry looks like workshop image.
Level 2 sentry has second gun and is smaller than default level 2 sentry, but shoots slower.
DISPENSER
Stat 1(Positive): Can stick to walls and ceilings.
Stat 2(Positive): Sappers have a low chance of "Falling off" and are deleted.
Stat 3(Positive): Fills up quicker than default dispenser.
Stat 4(Negative): Heals slower than default dispenser.
Dispenser fills 5 seconds before a default would, and metal gotten from one load is 10 less than default dispenser.
Model would be created by developer.
TELEPORTER
Default teleporters only. To complicated to develop.
Just my opinions, I do really want a new PDA though. I agree, regular sentries are pretty boring.