Hey, here's a thought, what about blocks with different characteristics and/or HP. Find a way to purchase them through credits from the supply bunker or from kills.

Like regular blocks have 10 HP, wood blocks will have 20 HP, stone = 50 HP, steel block 100HP. higher the HP, higher the costs to purchase.

Problems with multiple blocks are bogging down server performance and the amount of data a map takes up.

Currently a map is about 2mb just cause of sheer simplicity, but when you start adding new blocks this can add up without some ingenuity.

Right now focus seems to be on adding & balancing new weapons first before adding items to complement new needs that arise from said weapons.

On a second personal note, I would say with how physics work if you spent the time to make a fort out of the strongest materials {in your example this would be Iron or some such metal} most people would decide thats a lot of effort to destroy using explosives, and dig the dirt out from beneath it and just crumble your fort made of millions of kills/bucks of materials.

Any kind of "High-Quality" material that would take a lot of effort to amass and use effectively, would fall flat due to the fact you can destroy most key structures with enough time and a pickaxe.

What you want to focus on is reinforcement so the use of a slightly stronger material, that just makes you go out of your way to get it, is ideal.