For the limited-free-building contest I gave myself an even more extreme challenge: what could I do with only ONE block type? I chose nether brick stairs, in the gold challenge pack, because stairs are great.
It was an interesting but difficult challenge, with lots of twisting and turning in the air to get things in the right places, and lots of "oh but I can't do that without a slab" moments. By the way, lag sometimes means that stairs suddenly switch direction from the way you put them down! So I had to watch out because some carefully placed groupings would jump into new configurations without my bidding. A bit too frustrating to do ever again ... but it was fun once.