Situation Overview: A group of 16 (actually 100, but the others aren't relevant here) people have suddenly found themselves transported to a different world. It’s a hybrid setting, with tech and magic. The magic system is fairly standard(ish), but it's limited only to the teenagers in these displaced people, for plot reasons.
In the group of 16, there are only three teens with magic (one without, but again, plot). These three have access to Ice, Fire, and Earth magic, but can't actually use them very well yet. The earth mage (the obvious choice) can make walls to an extent, but can't build something with a roof that doesn't collapse, yet.
The 13 remaining people all have some access to equipment from our world through a system store, but can't currently afford any earth-movers or other heavy machinery. Access is limited to items the characters are intimately familiar with and priced according to familiarity and complexity. In other words, the resources available are pretty much only what they have on hand for the moment plus or minus a few small items.
Current tools and resources available: 16 people of various ages (see below for more info), one hand axe (hatchet), one entrenching tool, one sniper rifle (.50 cal), one pistol (.40 cal), five assault rifles (5.56mm), one first aid kit, one battlefield trauma kit (? not sure what the name is, or if it has one), many dead owlbat carcasses, also forests nearby. Access to water and food is covered through the system store.
Human resources: Two British material chemists, one fresh college grad with a biology degree, one surgeon, one civil engineer (road construction focused), one US Customs agent, two USAF pilots (rotor and fixed wing), one USAF pararescue jumper, one retired SEAL (medical-lost leg), one US Army armor officer, one USN Captain (destroyer skipper), the magical teens mentioned above, and the last teen who is more or less an insurgent/child soldier (she grew up in a warzone, scout/sniper specialty)
The location: The build site is on a rocky outcropping that's about 455 acres. It's bordered east and west with tropical forest (jungle), south has a smallish 20ft cliff (sheer drop) down to the ocean, and north has a small, brush covered mountain (around 1500-2000ft). Mountain hasn't been explored yet, nor has the jungle past a few hundred feet. The current camp is located on the northern edge, close to the mountain (about 20 feet from the base of the slope) and about equidistant from the jungles.
The problems/limitations: Only 12 hours of daylight, plus or minus. The daylight hours are somewhat calm, dangerous creatures can be encountered in the jungles but most avoid the rocky outcrop except to transit to the other side. At night a predatory species of owlbat (bat-like body and wings, owl beak and claws, sensitivity to sound and bright light, size can vary from house cat sized to medium dog sized) comes out in large numbers. They are less than friendly and can fly, obviously, so walls are of limited use. There is also a species of rock lizard that spits a viscous goo that acts like a high-explosive variant of natural napalm when set alight (the lizard can't light it, though). Moving camp isn't a viable option, the jungles are far more dangerous as the pistol and assault rifle are woefully ineffective on the larger wildlife (boars the size of a VW Bug).
How to build a credible (read: believable) simple fort in 12 hours?
Best answer would be one that can give a credible design for construction of a defensible campsite/compound while considering the limited resources, time, and location available. Must be able to defend (or at least protect) from aerial and ground predators. Ideally, it would be expandable over time.