I have made 2 versions of this block. The easy one (normal papercraft block) and the harder one.

EASY VERSION

This is just like a regular block.

HARDER VERSION

1. Cut out the template. The red lines are the cut lines and the dotted lines are the folds. (Don't cut along the dotted lines.)

2. Carefully fold the template in half and glue the 2 halves together including the base and its tabs.

3. Flatten the papercraft and wait for the glue to dry. This prevents the papercraft from warping. For example, you can put it between 2 heavy books (but make sure the glue doesn't stick to your books by putting 2 pieces of scrap paper on each side of the papercraft).

4. OPTIONAL ADVANCED STEP: Cut out along the top of the fire so there is no white on top. This makes the fire look really good, but it's quite hard to do. Try doing it with a hobby knife.

5. Assemble the block similar to a regular block (there won't be a top).

Credit to blackredevia for the Fire Block papercraft photo.