Random BrickColor, how about Random Materials?

BrickColor.Random()

Makes a Random BrickColor.

Making a random Material is harder only because Material is an Enum, as opposed to an Object like BrickColor.

--First, let's make a dictionary of the possible Materials:
local mats = {}
for _, v in pairs(Enum.Material:GetEnumItems()) do --Rather than hard code the values, populate the list based on the *current* Materials.
    mats[v.Name] = v
end

function MaterialRandom() --let's make this a function...
    return mats[math.random(#mats)] --And return one of the random members of that Table.
end