Ship Construction

Ships vary in construction, especially between the species. However, there are several constants, caused by laws of physics, tactical requirements of space battles, and variety of other things. With civilian ships being even more varied, since their consctructors do not need to trouble their heads over tactics. That's why we will focus on ships designed to fight and wage space wars.

Hull Shape

Surprise in space battles does not exist - that's the first thing candidates for navy officers learn. Ships emerging from Hyperspace cause a massive thermal flash, easily detectable by every Electromagnetic Sensor systemwide. The typical engines are capable of acceleration that is at best mediocre, with fleets taking weeks to reach inner system, all of this while being easily detectable. Before a combat occurs, both sides watch each other closely, easily detecting each other and planning many firing solutions, trying to outplan each other.
You simply can't surprise each other. The battle occuring accidentally, like by one fleet jumping exactly at each other's face, practically never happen. Even in hyperspace, the chances of this occuring are minimal, with both fleets always bumping at each other while being warned beforehand. That's why it is always possible to turn towards enemy in a way to make him face full possible firepower. That's why there is no real need to place your weaponry in a way that allows to fire at every direction possible. It is much wiser to actually concentrate your guns in a way that allows you to punch enemy in the face strong enough, with other equipment moved somewhere else.
Outer Colonies ships tend to resemble their progenitors that sailed on the seas of Earth in antiquity. They are long and cigaro-shaped, with artillery towers localized on their 'upper' deck, capable to move independently to taget multiple enemy targets at once. Missile launchers (with conventional rockets and LSK missiles) are on the upper deck (if small in size), while missile siloes (for SK missiles, or LSK in case of smaller units) placed neatly as a line through the ship's 'spine' on the lower deck. The rest of the ship is covered with shield generators, sensors, AV Defense, maneuver thrusters and so on, with main engines for acceleration and decceleration placed at the prow and the stern, together with magnetic shield paired generators.
Terran Federation on the other hand prefers a triangle-like, flat units (slighly similar to imperial destroyers from Star Wars), which allow to concentrate much bigger firepower on its upper deck, while strenghtening their resistance to enemy fire. However, it tends to make them slightly worse in terms of AV Defense that their colonial counterparts of similar tonnage, not to mention being noticably slower and have worse achievements in terms of magnetic shielding due to their different shape.

Classes/Variants/Configurations

All military spaceships are defined by their Classes, Variants and Configuration, which cover exactly 100% of armed ships in the Galaxy, regardless of all oddities.
Classes are absolutely basic types of ships, divided by their tonnage and projected usage on battlefields, including destroyers, cruisers, battleships and so on. They are absolutely not interchangeable, and play completely different role on the battlefield - destroyer for example can't replace battleship unless he wants to be annihilated in seconds.
Variants further define ship classes. They cannot be changed. While sometimes they tend to define simply size (Light Destroyer, Heavy Destroyer and so on), they are also variants that heavily vary in usage (Pocket Battleships, Battlecruisers and so on). However, at least to a point, their role on the battlefield isn't as divided than Classes, with for example Pocket Battleships capable of acting like the standard battleship - they will be worse at that, but won't be automatically annihilated.
Configurations are something that can be changed if one has chance to spend only few hours up to few days in field shipyards, or even by crew themself as long as they have access to resources. They can and should be changed, since they can be used to surprise enemy. They cannot be detected from a distance, so for example the defenders of the system have no idea if incoming fleet is full of missile configurated ships, or those that prefer artillery. This are simply ships with their equipment configured differently. They aren't even considered unique, hence for example US Navy heavy missile/escort Phoenix class destroyers. With missile/escort being possible to changed in a flash.