A new kind of weapon? I don't know, just build it with bricks. You have to be creative with making weapons. But if a kind of weapons roblox have, just search "Weapons" in the insert part.
im not sure how to MAKE your own weapons but i know how to put them onto your map if thats what you mean.
1.click Insert
2.Change from Bricks to Free Models
3.Search for the weapon you want(etc Pistol,Rocket Launcher)
there you go
-~Freepie~-