This is how I would play engineer as a defender on barn blitz. Immediately go out the door on the right at spawn. This should be in the attic above the second point. Set up a dispenser and a teleporter exit. Don't bother upgrading yet. There should be a full metal crate up there to help you out. Also, don't build too close to the stairs on the right and not too far forward at the ledge.
Now head towards the first point. Set up a level 3 sentry behind the rocks near blue's spawn. Try to live as long as possible. But you are going to die. They will have an uber and this is why building at the first point is bad against a determine team.
After you respawn, they should not have capped the first point yet. Head back to your dispenser and build your nest upstairs at point two. If you have time, head back to red's second spawn and set up the teleporter entrance. Remember don't build too close to the stairs. You can easily defend this point if a demoman and a pyro stay with you. Demo gets people who try to take your stuff out from the area across from you. They can also get people coming up the stairs, especially annoying pyros. A pyro stays with you for spy checks, air blasting away projectiles, and blasting away ubers if possible. Second point is a whole lot easier to defend than the first one.
If second point falls, then don't bother going to third. Start setting up at the fourth point.
As for attacking, go gunslinger till your team gets to blue's second spawn. Then switch to jag so you can build a level three near the third point. This keeps them locked up inside the fourth area. Less of a chance for them to destroy your tele.
Oh and build order. I put down a sentry, then a dispense, and finally the teleporter exit. Get the sentry to level two, then the dispenser. Then start working on teleporter to level 3. Finish the sentry and finally the dispenser.
The trick to playloads is to make sure the attacking teams medic is constantly down. They are guaranteed one uber at the beginning. But if their medic can't build another, then it becomes really hard to push.
Last night I was going on about point three being best to defend, but I made an error. It's point two. I wasn't even thinking about Engy strats, just general Medic and class placement. It's also a great point to run Kritz instead of Uber on the Heavy or Soldier, and a Soldier running Buff Banner does really well in that corridor.
As for Scout stuff, when you can't attack you play defense. Watch flanks, poke your head out for intel, etc. The Scout is actually a pretty good Spy checker since his speed allows him to quickly bump into enemy Spies faster. Plus you have Mad Milk now, which lights them up even when cloaked. And like other people have said, you can build up Bonk and that allows us a second uber to help with sentry pushes. Of course, the Wrangler screws this up a bunch, but it's better than nothing.
Finally, I got the demo files.
Match:
http://www.sendspace.com/file/6w95tp
Log:
http://www.sendspace.com/file/t73pt4
I haven't looked at it yet, but I've been told that the part of the game before the UGC config broke got corrupted. Still should leave us with a lot of footage. If someone wants to be brave and do a cast or just general recording to put up on youtube, go wild.
Edit: Also, talking some more with Team Mantrain, his guys could really use a scrim partner, and you guys are mean and suck. His team actually practices daily. I've set it up for either Thursday or Friday, whichever is better for us, at 9pm EST. I don't think I can actually make Thursday so if you play without me, be nice.