Tape several sheets of blank paper together with masking tape. Make the total area of paper large enough for the artwork you want to make. Put the tape only on one side of the paper. The other side will be where you make your poster artwork.
Sketch your artwork in pencil on the poster. When you are satisfied with your work, ink in the lines with waterproof marker. Cut out the poster artwork.
Add regular flour to a large bucket until it is 1/3 full. Slowly add water and stir vigorously until the paste is a thick, syrupy consistency. It should be thick enough to not run when you paint it onto a wall but not any thicker.
Brush a heavy layer of paste on the wall where you want to paste your artwork. Use a wide brush or a paint roller if the area is very large. Cover an area a little larger than your poster.
Apply the poster tape-side down to the pasted area. Smooth out bubbles and wrinkles from the middle outward with your hand or the brush. Make sure the edges are pasted down. If your poster has several parts, paste one at a time, starting with the lowest one first.