[Fyron]

Its no worse than SE4, where it was quite easy too. Just need to add new SM comps to create them, and add all the requisite bits for a new planet type (planetsize entry, stellarobjectypes entries, possibly xfileclass_stellar entries).

The Special Ability ID value in PlanetSize.txt is the basis for each type of constructed planet:

Name := Ringworld
Special Ability ID := 1

If you look up the Ringworld Placement Generator, you will see this number on its ability 1 Amount 1 value:

Ability 1 Type := Constructed Planet - Create
Ability 1 Description := Will create a Ring World around a star.
Ability 1 Scope := Space Object
Ability 1 Range Formula := 0
Ability 1 Amount 1 Formula := 1
Ability 1 Amount 2 Formula := 2

Amount 1 refers to which planet type will be created. You would need to make your new type have a "3" to make it distinct. I'm not positive what Amount 2 refers to; both RW and SW placement generators have it listed as 2.

Next, look at the req for gravity plating:

Ability 2 Type := Constructed Planet - Requirements
Ability 2 Description := Must have [%Amount2%]kT of Gravity Plating present at location.
Ability 2 Scope := Space Object
Ability 2 Range Formula := 0
Ability 2 Amount 1 Formula := 1
Ability 2 Amount 2 Formula := 10000

The amount 1 here refers to the custom group value for the type of req component you need (and the amount 2 refers to the kT total you need). Take a look at the Gravity Plating component:

Name := Planetary Gravity Plating
...
Custom Group := 1

The cables have a Custom Group value of 2.