More useful tiled layout that allows you to change a width/height of window.

You can use this module with the following in your xmonad.hs:

import XMonad.Layout.ResizableTile

Then edit your layoutHook by adding the ResizableTile layout:

myLayout =  ResizableTall 1 (3/100) (1/2) [] ||| etc..
main = xmonad def { layoutHook = myLayout }

For more detailed instructions on editing the layoutHook see the tutorial and XMonad.Doc.Extending.

You may also want to add the following key bindings:

, ((modm,               xK_a), sendMessage MirrorShrink)
, ((modm,               xK_z), sendMessage MirrorExpand)

For detailed instruction on editing the key binding see:

the tutorial.