If using cookies, add them to the food processor and pulse until you get a fine, corn meal like texture.
Same for the graham cracker crumbs, even if you use the crumbs, not the sheets, add them to the food processor and pulse until you get a fine, corn meal like texture.
Add graham cracker crumbs to a large mixing bowl, add the cocoa powder and mix.
In a small bowl mix water and sugar and microwave for 1 minute to create a syrup. Add the syrup to the crumb mixture and using a fork start mixing until combined. Using your hands combine all the ingredients, knead until they form a non-sticky easy to work dough, if needed add more warm water little by little, the texture of the dough should resemble play dough. Roll it into a ball. It should be easy to work with it, like with cookie dough.
Lay plastic wrap on the counter, it should be roughly 16 inches long, place the cookie dough ball in the middle and using a rolling pin, roll in into a thin rectangle. Mine was 10x12. Don't worry if the rectangle breaks into some spots, just take the broken pieces and press them into place with your fingers. The dough will have a play dough texture, so it's really easy to work with. Using a knife trim the edges.
In the bowl of an electric mixer, or in a medium bowl using a hand mixer, beat together butter and powdered sugar until fluffy, for 1-2 minutes. Scrape the sides of the bowl, add the condensed milk and mix until combined.
Using a spatula stir in the coconut flakes.
Transfer the coconut mixture onto the cookie dough sheet, distribute in an even layer, ½ inch from the edges. Starting from the edge that is facing you, using the plastic wrap, start rolling the cookie dough sheet with the coconut mixture into a roll. Press well to form a log, cover in plastic wrap and refrigerate for at least 1 hour before serving.
Do not remove the plastic wrap, store the roll in it, unwrap and slice only as much as you need to prevent it from drying out.