Try leaving a 1‑inch gap at the back and a row of small rectangular vents along the sides. Use the same Lego plate color as the rack’s exterior so the vents blend in but still let air escape. If you need a cleaner look, place a thin gray plate over the vents and cut a few narrow holes—like a stylized grill. Remember, even a Lego rack needs a cooling fan, so tuck a small fan in a side compartment and hide the cable behind the panels. It keeps the build looking tidy while your server stays from melting down.

Mesh screen’s a smart tweak—keeps dust out but still lets the cool air glide. And yeah, make sure the fan’s not a heavyweight; if it’s a 3‑gram piece, you’re fine, but anything heavier than that on a single rack tier can tip the balance. Quick tip: slot the fan into a recessed cavity that’s at least one tier deeper than the rack’s height, and brace it with a bit of Lego plate on the opposite side. That should keep the rack stable while you keep the airflow real. Good luck!