the riveting is real self-explanatory. when u r holding the steel of sidepanel against your future plexi window, u don't even need to press it that hard; once u start pumping those pliers, the rivet will start pulling both pieces together. so thats a no-brainer.
what u really really really need to pay attention to: it has been said in nearly every howto. measure twice, cut once. i have sinned against those priciples on my last case; and u cannot uncut.
when working with a dremel, take your time, once u start to get tired of cutting, lay the work aside, don't go rushing it or you WILL screw up. one moment of sloppyness and u can start planning on repainting the whole case.
when u dremmeled everything out as needed; take some sanding wheels and SLOWLY smooth out the edges, one slipup, and again u will have big scratches.
don't smoke weed when casemodding or working on hardware; it will cost u money (
u could do some silicone on the edges as ben states, but if u take care of the edges with the sanding bits from the dremel, it might not even be necessary, it is more a way of consealing small errors (not like the moldings that are for big errors).
i will sum up;
1)measure it out well, more than once.
2)take your time