Infrastructure represents a world's population as a whole, as well as their general ability to operate and support the construction of new structures. At the start of each player's turn, the infrastructure of each of their worlds is increased by 1 assuming it isn't already at the cap. Some buildings require a minimum amount of Infrastructure to be constructed. It also has an impact on the amount of time it takes to occupy and conquer the world. A world's starting infrastructure cap is equal to twice its fertility.
Structures require industry to create. Each structure has a cost that reflects how much of the local resources are required to construct it. A world has an 'allotment' of resource points each turn based on it's ore and gas values. Their building time is based on the world's construction rate. Construction 1 means your planet builds things at a speed of 1 per turn, meaning it takes 1 turn to build something that costs 1 resource point. You can build things that cost more then the local resources by either having logistics or simply taking extra turns to build it. If doing the latter, the world continues constructing the building at it's construction rate each turn until it is completed. Structures are started at the beginning of your turn and finish (or at least have your resources applied against) at the end of your turn. You may build multiple structures on a world, but you must divide the construction and resources between them. Your worlds all begin with 1 construction and 2 energy.
You upgrade structures to improve your world rather than building multiples of the same structure. Doing so is effectively treated as though you built an entirely new version of the structure. It increases the infrastructure, energy requirement, etc the structure already has. The cost of upgrading a building is equal to the building's base cost +1 extra ore or gas whichever is the highest (if they are equal you choose each time you upgrade). Upgrading may be done repeatedly, but the cost is cumulative. Upgrading takes the same amount of time as building a structure of the same cost. Example: You wish to upgrade your light manufacturing to it's next rank. It has a base cost of 1 Ore, so you spend 2 Ore to upgrade it, taking the time required for your world to construct a 2 value building. After which, the light manufacturing there becomes rank 2 and grants a total +2 construction bonus.
*Keep in mind that racial mods to structure costs are applied AFTER upgrade costs are determined.
Ships are produced much in the way structures are, but use the world's production value instead of its construction. When building a ship, you decide what systems you wish to assign to it, and how many ranks of each you would like. Then determine what size you would like the ship to be (size of course being limited by your shipyards; more on ship size below). After that you calculate cost by the following;
Ore: Ore cost of ship increased by 1 per rank of each of the following systems; Hull, Stealth, Sensors, Solid Weapon
Gas: Gas cost of ship increased by 1 per rank of each of the following systems; Shields, Engines, Warp, Energy Weapon, Explosive Weapon
Size: Gas and Ore cost increase by an amount equal to size rating. Note that engines and warp cost double on ships larger than size 4.
Ships come in various shapes and sizes, and races use various means to measure them. Larger ships are often slower and more expensive, but are also tougher and have more room for equipment and crew.
Size 0: Escorts and fighters. Ships of this size cannot board other craft and cannot be boarded. They also cannot initiate planetary invasions without another craft of at least size 1.
Size 1: Corvettes, Shuttles and colony ships. Ships of this size have 1 extra hull value.
Size 2: Frigates and science vessels. Ships of this size have 2 extra hull value.
Size 3: Destroyers and exploratory craft. Ships of this size have 3 extra hull value.
Size 4: Light Cruisers. Ships of this size have 4 extra hull value.
Size 5: Battleships. Ships of this size have 5 extra hull value.
Defenses are built exactly as ships are, but use the planet's construction value. Their size is limited by your total ranks in defense tech.
Note that defenses without weapons can 'defend' other defenses and ships. Such defenses can be declared to take the damage from enemy attacks for smaller craft and defenses. A defense can take a hit for 1 craft of a size equal to it, 2 of 1 size smaller than it, 4 of craft 2 sizes smaller than it, etc (Example a size 4 defense shield could take attacks for a size 4, 2 size 3's, 4 size 2's, 8 size 1's or 16 size 0's or any combination thereof). To defend a craft, it must be at 0 units of distance from the defense, any craft that leave the area, lose the benefits of this cover.
Ships and defenses will likely need repairs at some point. To repair a ship, it must be at one of your shipyards. Repairs costs are determined exactly as though they were rebuilding the craft (example: to repair 2 hull points would cost 2 ore). Repairs for ships use the planet's production value. Defenses are similar, but use the planet's construction value.
It is inevitable that ships and defenses you build will become outdated as your tech advances. You may choose to replace systems and/or add new ones. If you remove ranks from a system, you regain resources equal to 1/2 their value rounded down on that world this turn. Adding systems is treated as though you were building them from scratch, using the normal costs above. Defenses can likewise be upgraded and replaced.
You may choose to sell a ship you command at one of your shipyards or a structure on one of your worlds. It takes 1 full turn to decommission the selected ship/structure and you regain resources the following turn equal to 1/2 the total value of the ship/structure (rounded down).