I really love built-in benches, but I was not sure I wanted to commit because it’s not going anywhere after it’s installed. So instead of built-in benches, we made free standing benches that went in the corner and extend to the end of the table on two sides (coming together in the corner). This way we could move or replace without a renovation effort.
What we used:
1/2 inch by 3 1/2 inch wood planks, cut to length with support cross boards every foot on the underside of the bench.