I was an ace builder in Smaug 1.2 through 1.4a. I managed to teach myself nearly all aspects of building in that base because I was the only one in my MUD who was willing to do so. I think a few others came close, but not all that close.
So my question is... what documentation are you looking for? The HELP files in the 1.4 releases of AFKMud have plenty of information, and aside from that there's always trial and error. It's easier for me to say this though because I still remember how it all works.
So let me ask... do you want a HowTo on simple stuff? All you want to do is write rooms, objects, and mobs - basic stuff - no programs? That I can do. I need one for my own use anyways, as I have new builders coming on soon. MudProgs on the other hand are a little harder to teach via a guide. It is, essentially, a scripting language made to create a sort of 'AI' for your game. I can teach syntax all day, but concept and design is something that is only gained by experience.
As for the major command differences between SMAUG and AFKMud...
A brief run-down. I don't remember all the SMAUG counterparts. If any of these commands are not included, a quick cedit (command) create, cedit (command) level (desired level), and cedit save cmdtable will make them available!
Stat replaces the various m/r/ostat commands.
OR: show mob
OR: show obj
OR: show room
Can't remember which command it replaces - Displays all the (insert usage here) in an area or vnum range.
Note: oset, mset, redit -- Still the same command names, but different looks and syntaxes. HELP (command) is a great place to start with these!
find obj type
Finds the mob or obj that matches your criteria.
I think most of the rest are the same. There are various new commands that have been added to make the lives of builders much easier, but I won't go into all that here.
I hope this helps, and if I get the time I'll write up a guide