Is there a class like that in Pathfinder or 3e? Something where you can quickly build defensive positions or structures. I know there is something in Spheres of Guile that lets the area around be affected, but I'm looking for structure building.
A wizard with the right spells should work. Abjuration, conjuration and transformation spells will probably be the one you need to focus on. At low levels the structures may be temporary and may be actual structures, but you should be able to achieve something near enough. A sorcerer probably does not have enough spells but could work also.
To build permanent structures will probably require a high-level caster.
Pathfinder classes don't focus on a single gimmick, so there's no dedicated class for this, but it can easily be done with the right spell selection.
For example, Tiny Hut blocks vision outside-in, and Secure Shelter works as a bunker. There're also the various wall spells, starting with Wall of Ice, can creature structures. There's even a first elvel spell creatign a low wall, Expeditious Construction.
I don’t think anything does it from low level really. Earth and aether kineticists can pull it off eventually though.
Expeditious construction and expeditious evacuation are only 1st level. Using both of them together would allow you to create fairly decent fortifications. Expeditious construction is used to create a wall and then use expeditious evacuation to create a trench in front of the wall.
Incendiary runes and later explosive runes can create traps. Improved trap would also be a good spell for building fortifications, though it is a racial spell for kobolds. Unseen Engineers allows you to create lasting mechanical traps. Conjure deadfall is another trap creating spell.
When you get access to 4th level wizard spells you start to really be able to create fortifications. Secure Shelter is a 4th level spell as is illusionary wall. Most of the other wall type spells at this level are temporary, but still useful. 5th level spells gives you wall of stone, carve passage (Kobold spell), transmute rock to mud, and fabricate.
Look for combinations of spells that can accomplish what a single spell cannot. Transmute rock to mud combined with expeditious evacuation can allow you to carve out stone.
Other spells can be used to temporarily increase the structures. Mist and illusions spells can conceal your structures and give you other advantages. Attack spells can be used to aid the defenders.
Yeah, I got the Architect for my G.I.Joe like all classes army. Just wanted to see if there was anything else a little bit more focused on battlefield control. The Courser from Spheres of Guile also can do some of the things I'm looking for. I have about 145 classes. A few are Gonzo classes.