How to find the positions within a part?

The title may be a bit confusing, but let's take the default Baseplate for example. I'm making a part appear randomly on that Baseplate, so I used a part to take measurements of the ends of it, if that makes any sense. Is there a way to find the measurements via scripting? Comment if you are a bit confused.

Script:

function snow()
    while wait() do
-- got here try 1
    a = game.Lighting.Part:clone()
    print('cloned')
    for i,v in pairs(game.Workspace:GetChildren()) do
        if v.Name == "Baseplate" then
            a.Position = Vector3.new(math.random(-257,257), 200, math.random(-254,254))
        end
    end
    game.Workspace["Snow Script"].Script:clone().Parent = a
    a.Parent = Workspace
    a.Script.Disabled = false
    print('set')
    end
end

snow()