The room of requirements poster and house points poster were for my harry potter club. And the ten commandments poster was a presant my best friend gave me (:
Okay so what you need to do is get your white piece of paper and tea bag it. I used my fingers to spread the tea. The link below explains it well.
After you let the paper dry another option to make it look older is to burn the edges of the paper. I think it looks good if you put holes in it to add to the old effect.
Now useing a pencil first draw out the letters after your satisfied it looks like harry potter font go over it with sharpie. I think it looks better if you make some parts of the letters thicker (:
This is the website where I found the font... http://www.personal.psu.edu/klr5384/blogs/katies_blog/2012/04/recognizable-fonts.html
Now hang your poster up and enjoy (: