I did not count exactly how many disassembled pallets I've used to made this terrace (between 30 and 40). For the deck alone, I used 12 entire repurposed pallets. It costed me 50 €/$, and 1.5 months of work.
Deck from pallets; everything was saved: pallets, lumber and even nails. This cost me literally 0$. 9 pallets, 1 or 2 more to get some lumber to solidify the deck. I will finish it soon: tint, close all side, remove grass under it and add a table that will most likely be built with some more pallets.