I realize there is already a walls thread, but this idea is a little different so I thought it would be better to give it its own thread.
An upgrade system for walls.
There should be 4 types of walls in the game.
When you first start out, you should be given the first available type of wall in the game: The sandbag. After researching the upgrade, you can purchase an upgrade for selected walls on the map and upgrade them into fences. Then you should be able to upgrade them again into concrete walls. And finally, the last upgrade should be steel walls (something new to C&C). In addition, I believe steel walls should have a TS like component in that you can build things onto the walls (like garrisons for infantry).
-Upgrading walls should not be global. After researching an upgrade, the walls you've made should not change automatically. You should have to choose which walls in your base to purchase an upgrade for(using a grouping selection method). That way you can keep T1 walls in some spots where you don't want your heavier T2, 3 or 4 walls.
-It should cost money to upgrade IN ADDITION to the money you paid researching the technology.
Wall tier rundown.
Tier 1: Sandbags ($10 each) - can fire over, block infantry wayfinding, easy to destroy. All vehicles can run over.
Tier 2: Chain link fence ($20 each / $15 to upgrade from T1) - can fire through, block infantry wayfinding, blocks light vehicle wayfinding, easy to destroy. Heavy vehicles can run over.
Tier 3: Concrete wall ($100 each / $75 to upgrade from T2) - blocks all passing fire, blocks all ground unit wayfinding, takes a little effort to destroy. Heavy T3 tanks can run through them when weakened.
Tier 4: Steel wall ($500 each / $375 to upgrade from T3) - blocks all passing fire, blocks all ground unit wayfinding, very hard to destroy, cannot be run over, garrisons can be mounted on them.
-Creating sandbags is cheap, fast and easy.
-Upgrade system makes retrofitting your base easy.
-Benefits you if you want a cheap way to quickly obstruct an enemy's approach but also allows you to spend some money really fortifying a structure or position if you so desired.
-"Pro" players tend to shy away from walls because they believe they slow down the game. A balance would need to be made that make walls cheap, fast and easy to create so that they don't hinder your base building or unit construction but later allow you to quickly throw some money at it to upgrade them on the fly.
-Prices might need to be rebalanced.