Mechanical pencil... brilliant.
A tip for custom builders: please avoid purchasing the all-too-common $30 case/PSU packages. Spend the extra $40-60 (maybe even more) for a solid power supply, you will be glad you did. If you buy that case you just had to have and a power supply comes with it,
at least have it tested at your local shop before using it in your system. I've seen too many motherboards and/or other hardware wiped out by shotty power supplies (including several of my own parts, I'm ashamed to admit). Search our Hardware Forum and you'll see what I'm talking about.
Think about it this way, nearly everything on your computer is inside/attached to your case. Every electron that travels down every trace of every circuit board in your whole setup came from and is regulated by your power supply. Each and every one of the parts in your case can easily be destroyed if the power supply is not doing its job correctly. So, what sense does it make
not to spend the extra cash to ensure your power is coming from a source you can trust.