Placeable overlays

core/src/mindustry/world/Build.java

@@ -169,7 +169,7 @@ public class Build{
             return false;
         }
 
-        if(type.isFloor() && tile.floor == type){
+        if((type.isFloor() && tile.floor() == type) || (type.isOverlay() && tile.overlay() == type)){
             return false;
         }
 

core/src/mindustry/world/blocks/ConstructBlock.java

@@ -73,7 +73,10 @@ public class ConstructBlock extends Block{
         float healthf = tile.build == null ? 1f : tile.build.healthf();
         Seq<Building> prev = tile.build instanceof ConstructBuild co ? co.prevBuild : null;
 
-        if(block instanceof Floor floor){
+        if(block instanceof OverlayFloor overlay){
+            tile.setOverlay(overlay);
+            tile.setBlock(Blocks.air);
+        }else if(block instanceof Floor floor){
             tile.setFloorUnder(floor);
             tile.setBlock(Blocks.air);
         }else{