How would I go about modifying my computer tower's casing to mount 2 120mm case fans to it?

I pressume it's some hole cutting, drilling and screwing, then maybe a grill cover to place over the fans, but how would you recommend I achieve this?

I'm going to put an intake on the side-paneling section which you open up to have easy access to the internal compnents, then an exhaust on the top of the tower(grill would be highly needed in this area for when you might set something on top of your computer's tower when it's not in use).

These fans are nice(fans), and create quite the breeze on my face, but are unfortunately too big for the 3 provided fan mounts inside my case. This is good however because I can place 3 fans there that are the correct size.

Anyhow, I need to do some modding, any suggestions from experience?