Seriously, teams win and fall on either good engineers or lack of them. Spawn points, ammo crates are the more noticeable things, but well placed hedgehogs and similar can be very impactful too.
Except people who are building them receive absolute nothing for it, spending their time doing something not netting them any score whatsoever when they can be out there farming kills and score, thus XP.
Also there should be point rewards for everytime someone uses ammo crate you placed or spawn at your spawn point.
Plus remove ability for other friendly players to destroy stuff you build, especially said ammo crates and spawnpoints because if people do it for the lulz now, its gonna be worse if there would be any score for using them.
Also it would be great if we could get more building options, like higher sandbag walls, some sort of wooden thingy/box to step on, ladders etc.
Barricading a house is currently messy thing where you have to walk around window looking up to the sky all the time if you want actual barricade.