Fixes multi-z things.

code/modules/multiz/structures.dm

@@ -0,0 +1,86 @@
+//////////////////////////////
+//Contents: Ladders, Stairs.//
+//////////////////////////////
+
+/obj/structure/ladder
+	name = "ladder"
+	desc = "A ladder.  You can climb it up and down."
+	icon_state = "ladderdown"
+	icon = 'icons/obj/structures.dmi'
+	density = 0
+	opacity = 0
+	anchored = 1
+
+	var/obj/structure/ladder/target
+
+	initialize()
+		// the upper will connect to the lower
+		if(icon_state == "ladderup")
+			return
+
+		for(var/obj/structure/ladder/L in GetBelow(src))
+			if(L.icon_state == "ladderup")
+				target = L
+				L.target = src
+				return
+
+	Destroy()
+		if(target && icon_state == "ladderdown")
+			qdel(target)
+		return ..()
+
+	attackby(obj/item/C as obj, mob/user as mob)
+		. = ..()
+		attack_hand(user)
+		return
+
+	attack_hand(var/mob/M)
+		if(!target || !istype(target.loc, /turf))
+			M << "<span class='notice'>\The [src] is incomplete and can't be climbed.</span>"
+			return
+
+		var/turf/T = target.loc
+		for(var/atom/A in T)
+			if(A.density)
+				M << "<span class='notice'>\A [A] is blocking \the [src].</span>"
+				return
+
+		M.visible_message("<span class='notice'>\A [M] climbs [icon_state == "ladderup" ? "up" : "down"] \a [src]!</span>",
+			"You climb [icon_state == "ladderup"  ? "up" : "down"] \the [src]!",
+			"You hear the grunting and clanging of a metal ladder being used.")
+		M.Move(T)
+
+	CanPass(obj/mover, turf/source, height, airflow)
+		return airflow || !density
+
+/obj/structure/stairs
+	name = "Stairs"
+	desc = "Stairs.  You walk up and down them."
+	icon_state = "rampbottom"
+	icon = 'icons/obj/structures.dmi'
+	density = 0
+	opacity = 0
+	anchored = 1
+
+	var/obj/structure/stairs/connected
+
+	New()
+		..()
+		var/turf/above = GetAbove(src)
+		if(istype(above, /turf/space))
+			above.ChangeTurf(/turf/simulated/open)
+
+	initialize()
+		var/updown = icon_state == "rampbottom" ? UP : DOWN
+
+		var/turf/T = get_step(src, dir | updown)
+		connected = locate() in T
+		ASSERT(connected)
+
+	Uncross(var/atom/movable/M)
+		if(connected && M.dir == dir)
+			M.loc = connected.loc
+		return 1
+
+	CanPass(obj/mover, turf/source, height, airflow)
+		return airflow || !density