stops structures from being built on dense objects

code/game/objects/items/frames/table_rack.dm

@@ -59,7 +59,10 @@
 	if(istype(get_area(loc), /area/shuttle))  //HANGAR/SHUTTLE BUILDING
 		to_chat(user, SPAN_WARNING("No. This area is needed for the dropship."))
 		return
-
+	for(var/obj/object in OT)
+		if(object.density)
+			to_chat(user, SPAN_WARNING("[object] is blocking you from constructing the table!"))
+			return
 	if(!do_after(user, 3 SECONDS, INTERRUPT_ALL, BUSY_ICON_BUILD))
 		to_chat(user, SPAN_WARNING("Hold still while you're constructing a table!"))
 		return

code/game/objects/items/stacks/stack.dm

@@ -197,6 +197,12 @@ Also change the icon to reflect the amount of sheets, if possible.*/
 				to_chat(usr, SPAN_WARNING("The [R.title] cannot be constructed on a tunnel!"))
 				return
 
+			if(R.one_per_turf != ONE_TYPE_PER_BORDER) //all barricade-esque structures utilize this define and have their own check for object density. checking twice is unneeded.
+				for(var/obj/object in usr.loc)
+					if(object.density)
+						to_chat(usr, SPAN_WARNING("[object] is blocking you from constructing \the [R.title]."))
+						return
+
 		if((R.flags & RESULT_REQUIRES_SNOW) && !(istype(usr.loc, /turf/open/snow) || istype(usr.loc, /turf/open/auto_turf/snow)))
 			to_chat(usr, SPAN_WARNING("The [R.title] must be built on snow!"))
 			return