Layer stack up & thickness calculations for Metal-core PCB
No doubt there are many options, but the best thing to do is to find a board house that does Al PCBs and call them. Designing /w cooperation from your manufacturers is going to save you a lot of headache.

Here is a link to Henkel's Al PCB product datasheet, just to give you a heads up of what all is in a metal PCB: http://www.bergquistcompany.com/pdfs/techLibrary/tclad_2013_web_fullguide.pdf