This is a really random idea that came out of nowhere (seriously~) but still, it might be interesting.

Compound structure can only be created via blue prints, blue prints are unlocked via mission, NPC, badges, achievement and whatever other method aviliable.

Compound structure is created from existing planet structures on a planet, instead of artifact/CR/mineral. One a blue print is unlocked, you can use this similiar to an ability onto any planet that have the listed structures, and those structure will disappear yielding to a compound structure. In many ways, you can consider this as a structure upgrade like hypergates etc, but instead of upgrading one structure to one better structure, it upgrades multiple structures into one.

Compound structure cannot be extracted, but may be broken up. When broken up, it will turn back to some of its orginal components, thou some components will be lost forever.

Most compound structures, unlike regular structure, will have a durability count. And each sab/CCM/event will only reduce the durability by 1 if the dice rolls on it. It will be destroyed if durability reaches 0. They can be repaired at any time, usually with CR, thou some might require specific mineral or artifact to repair.
Optional: efficency might reduce when damaged.

The components of coupound structure are always unlimited structures, but they can be anything ranging from NPC drops to reserached/blue print structures to badge structures etc.

A few examples:
Topopolis Rings*2+space elevator*2+Astrobiology Ward=Astroring Habitat (size 13 Population +3000 +50% +3 artifact durability 3)

OB*8+Prejoran Slave Barrier+Nexus Barrier*2=Entity Shield(size 30 defense+20k, defense +50% No production, durability 10)

Spy uplink*2+Shadin Hypergrid Network+Hypersensor Satellite+Resonance Inhibitor+Counter-Intelligence Nexus+Inverse-Flux Satellites*2=Shadow grid spy network(size 20 +10 research +3 artifact +1000 Defense +2500 cloak durabiliy 2, not targettable by sab/CCM)

Isolation Bureau+Galactic Concord Station+Adumbrate Station+Interrogation Stronghold+Hypergate+Heist Dispatch Center=Central Command(size 6 All resource +7, Defense, attack, cloak +10% +1000 atk, +1000 def, +1000 cloak, durability 2, not targettable by sab/CCM)

Hypernode Brain+Star Lifter+Hyperforge Fabricator+Quasi-Chaos Minefield*2+Obviation Barrier*2+Inverse-Flux Satellites+Topopolis Ring=Prismatic Base (size 55 All production +14 +3000 Atk +3000 Def +1200 population +1000 cloak durability 7)

Would it make more sense to instead offer a 'set bonus' for having a specific collection of structures installed? That might work in a similar way.

That could work too.
In that case, the question is:
Is the set bonus an static amount or a bonus based on the number of components?

For example, if there was a OB+Prejoran Slave Barrier set that triggers at 4 OB.
Would 8 OB+PSB give the same bonus as 4 OB+PSB or more?
Furthermore, in case where it is scaled with components, would 8 OB+2 PSB count as one big set or 2 smaller sets?

In addition, if a structure is a part of multiple possible set, would it be counted multiple times?

For example, let's say there is also a "balance defense set" that requires 3 quasi mine, 1 topo ring and 3 OB.
If you have 1 topo ring, 4 OB, 3 quasi mine and a PSB on the planet, would it recieve the bonus from both sets (PSB+OB and balance) or just the first one to complete (by installation order). If it's only one being triggered in that case, would 7 OB allow both to trigger?


Something to think about when (and if) you are making set bonus

PS: I really feel Prejoran Slave Barrier should be in at least one of the sets, probabaly paired with Exotic Barrier and/or OB and with a fairly high bonus. There have been quite a few complaint about PSB being too weak, this should make it good again.