Medicine cabinet made from metal and aluminium 3" x 1" tube.
First thing to do is determine the size you need for your medicine cabinet. Mine is going to be approx. 24" wide x 36" high. I got my metal and aluminium from the Metal Super Market where they also cut it to the exact size I required. I used metal for the frame since it was cheaper and made up for most of the project. I used aluminium for the shelves as I did need as much but the expense versus weight made sense.
Building the frame.
I used 3" x 1" metal tube and bridging clips. The clips I got from work but you may be able to get them from a drywall supplier. I did find smaller ones at the Home Depot. Either way the clips are just to fast the frame to itself and fasten it to the wall. Final squaring and levelling will be done when mounting to the wall.
Preparing the metals.
You may have to clean the metals and prime. In my case the metal had oil on it. As per Tremclad's recommendation I used a TPS and then washed in soap and water. Use gloves and safety glasses for this stage. As for the aluminium I washed in soap and water and then wiped it with paint thinner immediately prior to painting. I primed the metal with Tremclad metal primer to prevent rusting. This is not the case for aluminium so I skipped the priming step.
Assembling the frame.
I made a jig out of wood on a sheet of plywood to hold the corners square and true while I fastened the clips to the metal. I used self-tapping framing screws as fasten the clips to the metal tube.
Adding the shelves.
Measure where you want your shelves and install them using the clips and self tapping metal framing screws. In my case I wanted three of them so I split the height in three to get the location for the two additional shelves hence giving my three usable shelves which consists of the bottom or the frame and the two added shelves.
I used a copper color spray can. Hold can about a 12" way and move around so the mist it produces gets all over the metal and screws. I also sprayed primer inside the metal tubes to prevent rust.
Adding the back lighting.
First determine where you want your lights to be. I used string leds I found at a Home Depot store I don't normally got. Now drill holes using a 1/8" bit as a pilot hole followed by a 1/2" bit to make the holes big enough to pass the wire and connectors. I made two holes on the right side, two on the bottom and one on the left side. To fasten the lights, the string lights did have glue on the back of them but since I reused them from the previous backlit mirror I had in my bathroom the stickiness was gone. I laid the lights face down on a rag and then sprayed the backside with 3M Super 77 glue. I then attached them to the frame where I wanted them, ran the wire from light to light through the frame inserting the excess wire in the tubes to hide them.
Attaching Drawer Sliders.
I picked up a pair of ball bearing drawer sliders that I found at PrincessAuto. I would recommend finding ball bearings draw sliders as they are sturdier and can handle the weight of the mirror fully extended. I centred them on the frame and then fasten them with self tapping metal framing screws. It is very important then you get the direction of the drawer sliders correct in relation to which side is top of the frame and which side the mirror will slide too. Keeping in mind the sliding direction of the mirror I then place the mirror face down putting the frame with the sliders on top drawer sliders face down. Make any adjustment to make sure the mirror is square and centred. Trace the sliders with a pencil. Remove frame and sliders. Remove the mirror portion of the drawer slider from the itself. I fasten that with regular metal framing screws using three on the the top and three on the bottom. My mirror frame is made from ABS so a self taping screw won't work very well here. Here I used four screws top and four on the bottom.
Mounting the frame to the wall.
Hopefully everything lines up correctly. I measure the distance from the bottom of where I wanted the bottom of the my frame to be and from the top of my vanity. I then cut a piece of wood at this height to use as a temporary support to hold the frame while I fastened the top left corner. I then attached my 4' magnet level to the mirror on the side to make it plum and on the bottom to make it level fastening the other side of the frame.
Remove temporary wood support. I found the best way to attach the mirror was to extend the drawer slider arms and then guide them on the drawer slider portion attached to the frame.