There are palisades which are realistically set up wooden walls. They just require ground to dig in.
Question: Can I actually dig into space in a parking lot, after removing the street surface material with a pickaxe?
Cause otherwise we would need something like that that could be build like a simple barricade, thrown together by all kinds of junk found in the road.
Perhaps we could draft vehicles into that as well.
NPCs should at the very least be able to be commanded to help pull a vehicle off the street and into a barricade.
That could then be crafted into a reinforced wooden barricade, which could be mounted with machine gunners and set fire too in case of a necessary retreat.
Its called fortifications in df. Liquids can pass through it, attackers can shoot through it if they stand immediately on the tile next to it. Shooting from it from a floor higher than the attacker is kinda bugger, as the game strangely removes distance from the defenders range when the attackers come.
But I imagine something like in Stronghold Crusader, where you were able to pour boiling tar on attacking units. You could also use fiery arrows to ignite tar pits you had before dug into the ground, though they are kinda expensive ingame.
Might not be what you are looking for, but this would be the other way around: A bookshelf hiding the access door to the hideout.
Bookcase HIdeout Entrance: http://de.wikipedia.org/wiki/Anne_Frank#mediaviewer/File:AnneFrankHouse_Bookcase.jpg
[quote=“CarlStayBack!, post:1186, topic:5570”]I’m not sure how easy this is to implement in the tiles, but I’d like to see pits treated the same way water and blood tiles are, so that connecting pit tiles look like a single large pit and not a bunch of separate pits as if a giant went crazy with a hole punch. This should also mean that anyone in a pit should be able to move freely to an adjacent pit tile.[/quite]
That would be something like ramps in df.
What he does is calculating the flow of water in a river that goes over different z-tiles (and forms a waterfall for example) only in its entry and end points of the reality bubble.
The functions get expensive again when you also ask to be able to dig around with the water (and form your own little channel for your row boat or something) that things get complicated and much more detailed. To first look into ramps, that move units one tile up or down and then one to a side might be interesting now that you ask for this feature.
The hauling part of the code should be brought to the point that we are at least THEORETICALLY able to ask an NPC to fetch an item (PATH finding totally taken out of considering in the implementation[/quote]
That should be possible over ramps AND stairs (which should allow @ to travel up and down), but not vehicles. Vehicles should be able to traverse ramps though.
I’m not really sure how this would work out if you were trying to pull a shopping cart upstairs (maybe you drop it and all the items spill out? But then what about 28 Days Later where that father of the child build that highly efficient entrance barrier of stacked shopping mall carts? But thats for C:DDA 3 probably 
The problem is that we are yet to improve different z-levels. We can look at df and see how they handle it. They handle it pretty well considering how deep down generated abandoned sites and former fortresses go.
Edit: Another suggestion while I’m here:
There are diving watches I’ve seen recently in a diving utility shop in Maldives. They could between 200+ USD to have measure depth, pressure and stuff.
A thermometer can be an app for the PDA, but then it has to be as unreliable as the Compass I have in my smartphone and.
But I think we should definitely check what App was there in a PDA.
And you know what I think? The First Handset they used in Matrix had a very interesting, simple interface. That might be nice to display the infos you want for the C:DDA, like temperature and all.
We gotta be careful not to create a god item in the PDA though…