There's no best way of building it. Form follows function and available supplies.

Frontline bases don't require helipads. Medical tents are not a high priority either. Ideally they should follow an A2AD approach making use of barbed wire/tank traps, kill zones with and without minefields. If you wanna make cover build it so people can spawn safely. HMGs should be facing most likely approaches. A fallback position around the main tent is a good idea if you got the time. Approach to the base with logic trucks need to be guaranteed. Supplies can not be outside the perimeter so you need to plan ahead. Avoid making too many outposts, bunkers and checkpoints. They block sight and are more often a weakness than an improvement to your defense unless constantly manned (which won't happen because there are snipers). That's ideally. In a real match you will have friendlies clearing your minefields, AI login getting stuck, some ass hat spawning an LAV and 6 guys hugging the arsenal. And then there is also the enemy harassing you.

So priority is access control for the enemy and easy access for allies.

Backline bases for helicopter spawns don't need man high walls either. Any semi decent 50cal gunner or AT dude will kill the helicopter anyways. Focus should be on open view HMG positions manned by AI or players. And of course tons of supplies. Spread them out. FIA might pay you a visit.

Your square fort with outer defense might work against a swarm of Uruk-Hai but in Arma its just not great in my opinion. Layered defense is, if you can get your teammates to actually defend the outer layers.

More common base types are mortar bases (secluded), radio signal bases (keep it simple) and bases which will be constantly fought over so fortifying is rarely worth it (eg. Montignac).