the way ive made is as follows:
1 cup water
add flour slowly and just break it up/stir with a spoon in the water mixture. Keep adding flour until the mixture won't take any more (until the flour wont break up/til its slightly chunky)
in another bowl bring 1 cup of just water to a boil.
when it boils, add the water-flour mixture. Stir constantly until the mixture gets thicker. If it gets too thick add more water, to thin, more flour. Stir it like that for a few minutes until it comes back to a boil and until the mixture is the consistency u want.
done
or you could just buy wall paper paste which is dirt cheap and already made