I had planned from the start to do a Pittsburgh stadium.
At first, I wanted to maybe do Three Rivers Stadium, which was torn down and replaced with (what is now) Heinz Field.
Three Rivers Stadium held both the Steelers (NFL) and the Pirate's (MLB) games.
This build would have been so hard, because the structure is perfectly round.
Because of this, I opted for Heinz Field (which was still really hard to build)
Because it is a football stadium, I just used the grass that is already in the world as a base. I chose a flat world so I wouldn't have to worry about finding a flat space that was big enough for my structure.
My first failure came VERY quickly. I built the entire field and half of my lines were one block off and did not connect. The first time I made the base field, it was to scale, but I decided I wanted the little dash lines, yard numbers, and enough space for a logo.