That, too, is good advice. As I implied, case-modding is one of the more ancient arts and practices of PC enthusiasts and veterans.
My project in the photos began with an old server case that a PC "Mom and Pop" store owner gave me for free. He was running a recycling operation out of his back door, and had a pile of cyber-junk, including cases. I didn't pay a dime for it. But the OP has a relatively new case -- a Corsair Carbide 100R. And he wants a window.
Suppose he does decide to cut a hole in his sidepanel. OK -- hopefully nothing lost there, but it's irreversible. He may spend a few bucks on Dremel cutting wheels or jigsaw blades. He cannot allow himself to screw this up. He should probably cover the case panel surface with tape, to avoid scratching it up.
But then, add a consideration for the next-door neighbors, who will have to suffer a bit for the clatter all this case modding can make. At least, that's a possible scenario. Unlikely that they would put a kibosh on the DIY project, because the disturbance may only last a few hours. But it is an aspect of the situation.
So, maybe ten bucks for tool parts, a couple hours of sweaty labor. Weigh that against just buying a new case that has a window in it.
At this point, I can't resist asking the question, since I posted my pictures. I wish I'd never let go of that Compaq DIY-mod, but my estranged brother last had it, and probably doesn't realize the value of what he has, so he may have discarded the whole enchilada. I won't go into detail about the various features besides the window, but I consider it a terrible loss.
So whaddya all think of my Compaq ProLiant mod? Is it cool?