Quoting CB
Hrmm... For example, you build a level one sentry, and proceed to pound metal into it. When it hits 200, you are quickly asked to press 1, 2, 3, or 4.
1 might give the sentry increased range, 2 might give it more fire-power, 3 might give it faster response time, and 4 might give it more hitpoints.
After two upgrades, your sequence of choices could create a sentry which is one of sixteen possible designs, and the enemy doesn't know which one it is before they encounter it.
You upgrade a level one dispenser, and 1 might give it increased range, 2 might give it faster recharge, 3 might give it faster output, and 4 might, again, give more hitpoints.
Making the right decisions with the dispenser could seriously help your team in some situations.
The same could be done for tele, but I'm having trouble thinking of what kind of options you could give them.
I like this. Adds a little complexity to the general sit and build. You need to know how the sentry will be used. Is it gonna be used to protect a long hallway? Then give it some added range. Gonna have a heavy sit on your dispenser? Give it some faster/larger health and ammo output.
A more elaborate sign of stickies being destroyed would be nice.
Haven't played much since the patch (damn finals, plus got pretty sick of tf2 recently) so I don't know how the spy change has affected things, but it sounds like it should allow a spy to hammer the enemy team more frequently.
Dec. Update discussion: Demoman Nerf, Spy and Engie buff
