this way

bot.py

@@ -78,11 +78,12 @@ async def d20(ctx):
 @bot.event
 async def on_message(message):
     if bot.user.mentioned_in(message):
-        if response == discord.File:
-            await message.channel.send(response)
         if random.randint(0, 10) == 5:
             pass
+
         response = await build_response()
+        if response == discord.File:
+            await message.channel.send(response)
         if response.startswith("<https://"):
             pass
         if response.isupper():