Hi there,
Dont know if you have seen this site
http://frank.bol.ucla.edu/almirrors.htm
but it describes very well the process of making an aluminium mirror. Dosent sound any harder than making a standard mirror from glass. I would imagine the same rules apply and a mirror of reasonable apature and focal length would be pretty straight forward for the ATM'er wanting to give this ago. It sure would make a "different" project!