List of tiers
Ideas for new buildings are found at Building ideas.
QUESTIONS TO COVER HERE:
Not really. But for additional details have a look at Automatic building development of residents, Building upgrades of marketplaces and branch offices and Manual building updates of companies and service institutions. Both articles are not completely uptodate, but might help to answer some basic questions or at least to raise new crucial ones.
Production: speed, capacity
Not sure about this one. The speed of collectors - especially carriers - is influenced by the streets used. The producers could work a bit faster with each tier or need less resources to finish their production - e.g. a lumberjack could make 2 quantities of boards from 2 quantity of wood in less time or 2 quantities of boards from 1 quantity of wood in the same time. The capacity of producers should be changed in two ways with each tier - a) the company's inventory should be able to store more resources to take more time before company is idling full - b) the amount of carrier units should be increased with each tier like the warehouse having 2 carriers in tier 2.
This one should be increased with every tier by a certain amount while this mainly affects warehouse and storage tents. As said in 1.2 the inventory of companies should also be slightly increased in every tier.
This will not change. Although buildings will upgrade or will be able to be upgraded (depending on how we will handle this issue) the dimensions will be the same. Newer versions of companies with bigger dimensions will be available via build menu as a whole new building, but NOT as an upgrade. Also have a look at Building dimensions.
Each tier will have its own tab in the build menu (the ones with the roman numbers).
gui looks? (different colors, slightly different style?)
This is currently NOT planned. Might happen in later development, but do not care about right now.
When is an tier reached?
As soon as all (demand) requirements of the current level ans these below are reached, a resident will upgrade its housing. Although it might only be just one of the residents this will unlock the new tier. An tier represents the maximum of "technology" available for a settlement, and although a resident might downgrade to a lower tier (due to a lack of happiness) or even all the current tier residents (like already reached settler tier, but due to downgrades only pioneer residents in settlement) this will NOT affect the tiers!
do they need building material for leveling up, and do they have to get it themselves?
Settlers need certain resources (depending on reached tier) to upgrade and yes, they have to get them on their own from the main square. Those resources should be defined as limited needs. Some more information on how this is meant to work can be found in the article about the Main square.
This will happen automatically if the player successfully set up the economy of the settlement. Depending on how we handle upgrades some buildings will need manual upgrades made by the player while residents will ALWAYS upgrade automatically as soon as all needs are fulfilled (including the availability of the resources needed to upgrade).
The gfx sets for each tier differ.