The bathroom did not have a light switch or outlet. The light and outlet was integrated into the old medicine cabinet. There also was no ceiling vent/fan/light. We spent a lot of time on this and my son Tony had to spend a good amount of it in the attic for the vent/fan portion. It was not easy as there is practically no room to move around up there. The space is so tight that we couldn't even get the vent/fan installed in the middle of the ceiling.
This one was a little out of my comfort zone but between some expert advice and trouble shooting on my son Tony's part we got this all to work. First I bought 25 foot of 14-2 Romex cable which is rated for 15amp circuits. I used a fishtape to run a line of romex from where the Ceiling vent/light/fan would be down through the wall where the original main feed was. I then cut a hole for the light above the medicine chest and ran another line of romex from the light fixture down the same route giving me enough length on both of them to reach were I was going to install the switches and outlet. Last but not least I wire nutted the original feed to another length of romex to run to the new box.
Here is a YouTube Video on explaining what a fishtape is and how to use it. I would not of been able to do this job without using a fishtape.
I will try and give a better explanation on the wiring below:
After removing the old medicine cabinet all I had was the main feed (Black and White) wires coming through a hole in the back of the medicine cavity. I ran my fish tape up this hole and up through the attic where my son attached the romax for me to fish back through. I then used my hole saw I used earlier for the bathroom door, door knob install to cut a hole where I was going to mount the light above the medicine cabinet. I used my fishtape using the same route taken earlier to fish that length of romax down. I then twist nutted the black and white wires from the main feed to another length of romex to lengthen the cable. So I now had three strands of romex (1 for the light, 1 for the vent/van/light and 1 for the Main Feed). I used my hole saw to drill another hole in the side of the medicine cavity to run my wires down to my 3 gang box. After cutting out the drywall for the box I found that I had a 2x4 running horizontal between me and the feed hole I had made above so I had to use a 1 inch spade bit to put a hole in it. I then ran my fishtape up through the gang box cavity through the 1 inch hole and out my access hole to fish the wires back down.