Custom Chatbox

[PortalGod]

How would i go about making a custom chatbox?
So far, i have:
[lua]
function GM:StartChat(ts)
//nothing appeared if i tried to draw with this, so i hid it.
return true
end

TypingChat = false
alpha = 0

function GM:PlayerBindPress(ply, bind, pressed)
if(string.find(bind, "messagemode") and pressed) then TypingChat = !TypingChat end
end

function GM:HudPaint()
//Chat
if not(TypingChat) then
if(math.ceil(alpha) == 1) then
alpha = alpha - 0.01
else return end
end
if(math.floor(alpha) == 0) then
alpha = alpha + 0.01
end
draw.RoundedBox(8, ScrW()/2 - 125, ScrH() - 250, 250, 200, Color(150, 150, 150, alpha*150))
draw.RoundedBox(4, ScrW()/2 - 120, ScrH() - 73, 240, 18, Color(100, 100, 100, alpha*150))
end
[/lua]

But that acts really weird.
Can anyone give me a starting point?