A note on A/D Façades.
The theme is typically based off an important resource. Weapons, fuel, food, transport and communications are probably the main 5. Once chosen, you can begin to shape your aesthetics to meet the needs of replicating X type of facility.
When applying 3 stages it is easier to break up progression, whilst single stage A/D can be a little trickier in applying hints of progression to players. But it can be defined as such: sparse huts and out house storage sheds, into more solid structures that probably handle raw materials and equipment, then onto more developed and permanent structures (made out of metal and concrete as opposed to wood) that are likely used for refining or the later stages of resource X's life. Be it a firing mechanism for weapons, distillery for fuel, depot for food etc.