Jobs initially wanted a 40-foot cube, leading the designers to set up a scaffolding mockup of the building. However, once Jobs and other Apple executives went to go see the mockup, all agreed that it was too big and obscured the vision for the store.
I think that story really illustrates what made Steve Jobs great.
While he always dreamed big - it wasn't ridiculous dreams. He didn't say "build me a 100 foot cube." He also never hedged his bets: he knew enough to know that 10 foot cube would look like a shed. But he was also flexible enough to know that a first idea (even when they were his first ideas) can be improved upon.
Its also amazing how "hands on" Jobs was. That he instinctively knew that Apple's Fifth Avenue store was going to have a tremendous impact on how Apple was going to be seen. That, even if they didn't go inside, millions of people from around the world were going to see this totally unique, totally cool storefront in the center of the most important city in the world.