Given that the game already tracks cargo tonnage, I'd rather just ignore the size of the unit within altogether, and count its mass as part of the ship's cargo allocation. That way you simplify designs a bit, because you don't need to worry about just how big the bays are - a mech bay stores one mech, and can do orbital drops etc. with it, while the mass of the mech is a load on the ship as a whole.

I have an old half-written proposal for major aerospace changes, but this part is complete. Crew need places to sleep aside from the bays themselves, if only to cover life support needs etc.

`Mech Bay: 20 tons. `

Vehicle Bay: 20 tons.

Fighter Bay: 20 Tons.

ProtoMech Bay: 10 tons.

Infantry Bay: 5 tons.

Small Craft Bay: 50 tons.

First-Class Cabin: 10 tons, luxurious

Second-Class Cabin: 7 tons, comfortable. Officers require at least second-class cabins.

Third-Class Cabin: 5 tons, serviceable. Ship crews require at least third-class cabins.

Bunk: 3 tons, spartan. Any passenger staying in a bunk for more than a week gets -1 to all rolls(piloting, gunnery, repairs, etc.) until they have been off the ship for one full day.

(Note: These quarters are heavier than BT norms, but they match pretty closely with weights from real-world passenger liners, as far as I could tell.)

I've also come up with a suggestion for repair facilities, which are intended to go along with the above, but also provide some economies of scale for dedicated repair arrangements. Hopefully that'll help explain why DropShips tend to specialize a bit. Again, these are just the weight of the facilities, not of the units therein.

`Mech Repair Facility: 100 tons(1 mech), 300 tons(4 mechs), 800 tons(12 mechs), 2000 tons(36 mechs). `

Vehicle Repair Facility: 100 tons(1 vehicle), 300 tons(4 vehicles), 800 tons(12 vehicles), 2000 tons(36 vehicles).

Fighter Repair Facility: 100 tons(1 fighter), 300 tons(4 fighters), 800 tons(12 fighters), 2000 tons(36 fighters).

ProtoMech Repair Facility: 50 tons(1 protomech), 150 tons(4 protomechs), 400 tons(12 protomechs), 1000 tons(36 protomechs).

Infantry Equipment Repair Facility: 20 tons(1 squad), 60 tons(4 squads), 150 tons(12 squads), 400 tons(36 squads).

Small Craft Repair Facility: 200 tons(1 small craft), 600 tons(4 small craft), 1500 tons(12 small craft), 4000 tons(36 small craft).

Sick Bay: 100 tons(10 patients), 300 tons(40 patients), 800 tons(120 patients), 2,000 tons(360 patients). Includes one operating theater per 10 patients.

Small DropShip Repair Facility(up to 2,500 tons): 500 tons(unpressurized), 1,500 tons(pressurized).

Medium DropShip Repair Facility(up to 12,000 tons): 1,000 tons(unpressurized), 3,000 tons(pressurized).

Heavy DropShip Repair Facility(up to 50,000 tons): 2,000 tons(unpressurized), 6,000 tons(pressurized) - must be in Space Station or unit of at least 100,001 tons.

Assault DropShip/Light JumpShip/Corvette Repair Facility(up to 100,000 tons): 4,000 tons(unpressurized), 12,000 tons(pressurized) - must be in Space Station or unit of at least 250,001 tons.

Medium JumpShip/Destroyer Repair Facility(up to 250,000 tons): 10,000 tons(unpressurized), 30,000 tons(pressurized) - must be in Space Station or unit of at least 750,001 tons.

Heavy JumpShip/Cruiser Repair Facility(up to 750,000 tons): 30,000 tons(unpressurized), 60,000 tons(pressurized) - must be in Space Station or unit of at least 1,500,001 tons.

Assault JumpShip/Battleship Repair Facility(up to 1,500,000 tons): 60,000 tons(unpressurized), 180,000 tons(pressurized) - must be in Space Station.

ArkShip/Dreadnought Repair Facility: 100,000 tons(unpressurized), 300,000 tons(pressurized) - must be in Space Station.