Use two 4-bit Adder as building blocks for a 8-bit Adder. Your 8-bit Adder should indicate whether the result can be represented with 8 bits. You will notice that some little modification is required to the 4-bit Adder that was implemented in the video (Hint: There's a reason why only Full Adders were used for the 4-bit Adder).

Make a nice demo circuit for your 8-bit Adder. Maybe something like this: