Honestly, I think that if you want to go truly custom, the only thing that really needs to be standard is the helmet, and even then, it doesn't have to be a precise copies of the Fetts.
A bit of research about the Mandalorian people has shown that their armor has changed over the years, as is shown in this pic, which I found on wookieepedia.
All of these are technically correct forms of armor, they just aren't from the movies, so don't expect to use it to join the 501st.
I'm currently working on a custom myself, and am designing it towards a Mandalorian Sniper/Scout, so the armor I'm thinking of will have some resemblance to the Fett style of armor, but it definatley won't be a carbon copy.
Hope this helps