if you want a "grid" so you can align things
or so you can mark where a 6x6 or 2x3 or? rollfilm holder
would be to make your composition that much easier ..
make a grid on a sheet of paper and go to your friendly
copy shop and have them print it on clear film, its cheap
just slide it on top of your glass under the clippy things
and there you go, an inexpensive grid ...

have fun !