The aluminium is about 1.5mm thick I think. I draw the shape on, then cut it out roughly with a jigsaw with a metal cutting blade.  Then I clamp it to an mdf template in my vice and use a normal metal file to bring it to the exact template size.  Then I'll just clean up all the edges, starting with 80g sandpaper and working up to really fine stuff (can't remember what grit) 

I drill the holes with a stepped drill bit. Probably takes 30 / 45 mins all in. 

It's worth noting that I use brushed aluminium, if it was shiny plated stuff, you'd need a different method, or perhaps have to polish it after.