Spoiler
Custom map 7, the city one where the defenders are defending a large building with the flag on the front balcony, is complained about all the time, it's p badly designed and attackers can almost never win.
There are two main ways into the upper floor of the defender building, the stairway which can easily be blocked with plank spam and the ladder to the back balcony which many attackers don't even know exists because of it's rather "hidden" access route! I'd suggest putting a hole in the wall on the left side of the defender building to let people circle around the building and find the rear balcony ladder easier to put more pressure on the defenders.
Attacker sappers spend a lot more time glitching their team onto nearby roofs at the attacker spawn rather than destroying defenses, the rooftop attracts a good 1/5 of the attacker team every round to ineffectively snipe at the well covered defenders and basically guides them to not help their team. The roofs could be blocked and snipers could relocate to the large barricade in front of the building where they perhaps might hit something or even take part in the attacking.
Please allow explosive crates for attackers because the stairwell can be blocked off entirely with plank spamming.
Also the spawn placement is a problem here as it is with many other maps. The defender spawns are placed right next to the flag or directly on the route to the flag which means that they will be spawning in the middle of attacking enemies if they manage to push to the flag. Spawns could be placed in more secluded areas (houses, back rooms, rooftops) behind the flag with multiple approach routes to the flag like in the vanilla maps so that defenders can try to make a counter attack to reclaim the flag rather than be spawnkilled constantly until the round ends. (For example the defender spawns in custom map 1 could be moved further back to the small cottage at the back of the map rather than around the flag and in the courtyard which are under constant attack)
edit: (Custom map 7 will too turn into a defender spawnkilling nightmare if the attackers by some miracle manage to pass to the upper floor, perhaps move defender spawns to the attic or into a new separate wing of the building)
The only reason for which attackers can't win is the plank spamming which will be adressed as stated many times either by limiting the number of planks or by deleting planks. Allowing crates isn't possible as the house is entierly destructible.
As for spawn points, having people spawn on the roof would be ridiculous and completely ineffective. How could you defend the flag from there?
Spawn points have already been changed many times on many maps. That never prevented players from whining because they got spawnkilled. And no vanilla map has ever completely protected players from spawnkilling. Spawnkilling is part of this game mode because there is no spawn protection in this game. Since Minisiege has small maps, it's even harder to prevent spawnkilling.
The farm at the Russian fort is not only too far from the flag and the walls, which would decrease the ability of players to defend, it's also behind the map limit, so if players spawned there they couldn't be reached by the attacking team, which isn't an acceptable option.
On some vanilla maps the spawns are placed behind the flag. But most of those maps are defended mostly by their walls and by the length that separates attackers from the flag. I refuse to have players run for 2 minutes before being able to see the actual fight, most likely to die from a bullet.