Over at MODTHEBOX! they have two Cutting Edge Acrylic Window Kits which they not only look at but show you how to install them.

Each individual kit is sealed in a plastic protective bag and includes a two-page set of detailed instructions, a washer and an installation tool. The top mount window measures 30.5 cm long and 15 cm across at the widest point and can be ordered with or without the hole pre-drilled for a 92mm fan. The side window measures approximately 34 cm top to bottom and should fit most mid-tower or server cases on the market. The side window kits can be ordered with or without a pre-drilled hole for 120mm or 92mm fans depending on your preference.