The perl source distribution is available from 
   http://www.cpan.org/src/index.html

For the easiest build of perl under Cygwin, do the following:

(1) read
       *(a) README.cygwin from the perl source distribution
       *(b) read build-instructions.charles-wilson
        (b) read build-instructions.sebastien-barre
        (c) read build-instructions.steven-morlock
        (d) read build-instructions.steven-morlock2
        (e) read build-instructions.teun-burgers

(2) prepare the source
        (a) unpack perl source distribution in /usr/local/src
        (b) copy perl5.005_03.patch into /usr/local/src/perl5.005_03/
        (c) cd /usr/local/src/perl5.005_03
        (d) chmod -R +w *
        (e) patch -p1 < perl5.005_03.patch

(3) get ready to build
        (a) cp cygwin32/* .
        (b) cp gcc2 /usr/local/bin
        (c) cp ld2 /usr/local/bin
        (d) cp hints/cygwin32.sh config.sh
        (e) sh Configure -d 
                (automatically does a make depend)

(4) build and install
        (b) make
        (c) make test
        (d) make install

To customize, look around in the patchfile or ignore the patch and follow the build-instructions.* directly. If you want to edit the paths in the patchfile to reflect your system, search for "/usr/" within the patchfile.

* MUST read.