The re-issued Tamiya 1/25 scale Centurion might be an option - kit #30614
It's a honking big kit and can be assembled without the interior to reduce the number of fiddly bits. Of course, you'd have to deal with the link to link tracks, but they're vinyl and assembled with steel pins (already cut to size). It's also "old school" Tamiya and should assemble clean with good kit design and engineering all around.
Other than that, there're a lot of 1/6 scale options. None are cheap, but it's about the largest sized armor you can get into.
DML makes a bunch of 1/6 kits, all the way from weapons to full tanks, like the 1/6 Sherman.
Armorama::DML 1/6th Scale Sherman Tank Build Blog A lot of the 1/6th scale stuff is constructed as R/C, but most of it can be built as static models, too. Again, not cheap, but certainly large and generally easy to handle parts-wise.
HTH,
Editor-in-Chief
Wanted to get it in "armor", and wasn't used to the forum yet. If you are a moderator, please feel free to move or delete, as needed. Sorry............
There is also the Revell 1/32 Sd.Kfz. 232 armored car car kit. It's cheap, it's a big kit and very easy to assemble. It also comes with a couple of crew figures. It should be a perfect first armor kit.
