how do I make a boundary around a map?

I want to make a boundary around my game so no one falls out but how do I set it up?

This isn't really a scripting question, but I guess I'll answer it.

--[[
Insert a part.

Resize it around one side of the map.

Repeat until all sides are covered.

Insert another part.

Put it as a ceiling to the map.

Select all parts and set their Transparency to "1" in the properties.
]]--

while wait(5) do
print("You've successfully learned how to actually use studio!")
end