To be correct, Elysia is the name of a gas giant planet in Metroid Prime 3: Corruption where an ancient alien race called "Chozo" which do have a bird-like appearance have established a huge research and observation facility floating in the planet's stratosphere. This skytown was actually the most notable inspiration for this project.
Here you get some information about the structures, units, upgrades and abilities you have access to in the game.
From Construction Nodes to the Cluster
Construction Nodes are pre-placed objects with a specific distance to each other to build up a Construction Node Cluster (CNC). Once you have access to a node you will be able to summon structures via these nodes.
Nodes are initially inactive but summoned structures nearby activate them. At the very beginning you normally cannot build everywhere but with each structure you build you get access to new node locations. Also different CNC sciences and Node Bridges will help to reach new locations.
If a structure has been destroyed or sold an appropriate node will appear which activates itself after a short delay. But this is not always the case!
Nodes can also be influenced by traps which can have different effects. One trap, for instance, re-configures a node back to a very basic design resulting in no build options at all. However, you always have countermeasures against traps.
Strato Buildings

Nexus Tech Structures
They will be summoned by a Nexus Node around the Strato Nexus.
Both, the Strato Nexus and its fortifications, the Nexus Tech Structures, build up Sky Town capital!
(to clarify: a Science here refers to a global player based upgrade, just another name)
Defense Towers
Floating Towers
Solid Towers
Hybrid Towers
Tech Buildings
- Amplifier: Uses Core units to buff towers nearby and debuffs Creeps in range.
+ effect depends on Core unit - Core Depot: Production facility of Core units.
+ Ability ???
+ Upgrade ???
+ Upgrade ???
+ Upgrade ??? - Technology Transmitter: Multi-upgrade center that provides upgrades of other structures which do not exist or are not buildable on a certain map.
+ variety of upgrades