Schemdownloadlink (untested)

SchematicSystem_Main/src/de/steamwar/schematicsystem/commands/GUI.java

@@ -126,6 +126,10 @@ class GUI {
                     p.closeInventory();
                     changeType(p, schem);
                 });
+            inv.setItem(5, SWItem.getMaterial(""), "§eDownload", click -> {
+                p.closeInventory();
+                SchematicCommand.download(p, schem);
+            });
             inv.setItem(6, SWItem.getMaterial("SKULL_ITEM"), "§eMitglieder", click -> {
                 p.closeInventory();
                 delmembers(p, schem);

SchematicSystem_Main/src/de/steamwar/schematicsystem/commands/SchematicCommand.java

@@ -308,6 +308,15 @@ public class SchematicCommand implements CommandExecutor {
         }
     }
 
+    static void download(Player player, Schematic schematic){
+        if(schematic.getSchemOwner() != SteamwarUser.get(player.getUniqueId()).getId()){
+            player.sendMessage("§cDu darfst nur deine eigenen Schematics herunterladen!");
+            return;
+        }
+
+        player.sendMessage(DownloadSchematic.getLink(schematic));
+    }
+
     private void addmember(Player player, String[] args){
         if(args.length < 3){
             help(player);