Overhead HP bar Surface properties inlet and studs?

Added a set of property modifications regarding the surfaces not being smooth for your script... I noted them with comments

print 'Hello world!'

--Created by XanthicDragon
--Inspired by "Sword Art Online: Burst"

game:GetService("StarterGui"):SetCoreGuiEnabled("Health", false)


local Players = game:GetService("Players")
local Player = Players.LocalPlayer
local Character
repeat
    wait()
    Character = Player.Character
until Character

local Human = Character:WaitForChild("Humanoid")
coroutine.resume(coroutine.create(function ()
    while wait() do
        if Character:findFirstChild("Health") then
            Character.Health.Disabled = true
        end
    end
end))

local red = Instance.new("Part", Character)

red.FrontSurface = "Smooth" --these here
red.BackSurface = "Smooth"
red.LeftSurface = "Smooth"
red.RightSurface = "Smooth"
red.BottomSurface = "Smooth"
red.TopSurface = "Smooth"

red.Material = "Plastic"
red.BrickColor = BrickColor.Red()
red.FormFactor = "Custom"
red.Size = Vector3.new(4, 0.5, 0.5)
red.Anchored = true

local green = Instance.new("Part", Character)

green.FrontSurface = "Smooth" --and these too
green.BackSurface = "Smooth"
green.LeftSurface = "Smooth"
green.RightSurface = "Smooth"
green.BottomSurface = "Smooth"
green.TopSurface = "Smooth"

green.Material = "Plastic"
green.BrickColor = BrickColor.new("Lime green")
green.FormFactor = "Custom"
green.Size = Vector3.new(1, 0.5, 0.5)
green.Anchored = true
local gmesh = Instance.new("BlockMesh", green)
gmesh.Scale = Vector3.new(4, 1.2, 1.2)

local angle = 0
game:GetService("RunService").RenderStepped:connect(function ()
    angle = angle + 3
    local MH = Human.MaxHealth
    local HP = Human.Health
    if MH ~= math.huge then
        if HP < MH then
            Human.Health = Human.Health + 0.05
        end
        green.BrickColor = BrickColor.new("Lime green")
        gmesh.Scale = Vector3.new(((HP/MH)*4)+0.05, 1.05, 1.05)
        gmesh.Offset = Vector3.new((HP/MH)*2, 0, 0)
        red.CFrame = Character.Head.CFrame * CFrame.new(0, 2, 0) * CFrame.Angles(math.rad(angle), 0, 0)
        green.CFrame = red.CFrame * CFrame.new(-2, 0, 0)
    else
        green.BrickColor = BrickColor.Yellow()
        gmesh.Scale = Vector3.new(4.05, 1.05, 1.05)
        gmesh.Offset = Vector3.new(2, 0, 0)
        red.CFrame = Character.Head.CFrame * CFrame.new(0, 2, 0) * CFrame.Angles(math.rad(angle), 0, 0)
        green.CFrame = red.CFrame * CFrame.new(-2, 0, 0)
    end
end)

This is one of the ways you can do this. Alternatively, you can have the bricks already made prior and simply clone them from a folder or lighting or w/e people store stuff in these days.

example:

local red = game.ServerStorage.Folder.red:Clone()
local green = game.ServerStorage.Folder.green:Clone()

of course, the folder isn't necessary but it'd look nicer.

I cant guarantee that the cloned variables won't bug out if you decide to mess with its CFrame and whatnot, but give it a shot if you find the first solution unappealing.

You can set the surface type of a part by using something like the following.

part.TopSurface = Enum.SurfaceType.Smooth
-- but, you can also declare it as a string.
part.TopSurface = "Smooth"
-- or use the Enum value
part.TopSurface = 0

The surface property names for all BasePart classes are TopSurface, BottomSurface,LeftSurface, RightSurface, BackSurface, and FrontSurface. BasePart BasePart is the base class for physical parts such as Part, WedgePart, MeshPart, and more.

Enum.SurfaceType reference: http://wiki.roblox.com/index.php?title=API:Enum/SurfaceType

BasePart reference: http://wiki.roblox.com/index.php?title=API:Class/BasePart