I just built a new windows version today. It doesn't contain new features, I just wanted to test whether the recent code changed had any adverse effects on the window code.
You need a cygwin environment to build SheepShaver or Basilisk (at least, that is what I use). Besides the obvious compiler, you need some extra packages installed as well (cvs etc). Alas there is no overview of all required packages.
You install SDL (I use 1.2.14) in Cygwin and use the same commands as in Unix/OSX. Below are my build steps:
#Install SDL: download the source and do:
./configure --disable-shared --prefix=`pwd`
#You need to cd into the SDL folder every time you start cygwin and export the path to sdl-config to build #SheepShaver, so SDL libs and sdl-config file can be found
#Download the Basilisk and SheepShaver source
cvs -d :pserver:email@example.com:/home/cvs/cebix login
#(password is "anoncvs")
cvs -d :pserver:firstname.lastname@example.org:/home/cvs/cebix checkout BasiliskII
cvs -d :pserver:email@example.com:/home/cvs/cebix checkout SheepShaver
./configure #(there are no extra parameters when building in windows)
#You might run into a problem with the GTK version check, at or around line 3977? in configure. Just comment out #the 6 lines in the file related to the check, and things will work out.