Short answers, pulled from the story.
Minas Tirith rises approximately 700 feet from its base to the Citadel at the seventh level. The Tower of Ecthelion atop the Citadel adds another 300 feet, placing its pinnacle roughly 1,000 feet above the surrounding plain.
The shape of Minas Tirith in Jackson's film adaptation was based on the tidal island and abbey of Mont Saint-Michel in France. Concept designer Alan Lee also gave the city an appearance reminiscent of Byzantium or ancient Rome.
Tolkien and scholars have linked Minas Tirith to Troy, Rome, Ravenna, and Constantinople. In a 1951 letter, Tolkien himself described it as "the Byzantine City of Minas Tirith", directly associating it with Constantinople and the Byzantine Empire.
The White Tree stood in the Court of the Fountain at the heart of Minas Tirith's Citadel and served as the symbol of Gondor. It remained dry and dead throughout the centuries of the Stewards' rule, and Aragorn brought a living sapling of it into the city upon his return as king, symbolising the rebirth of the monarchy.
Minas Tirith has seven walls, each encircling one of the city's seven levels. Each gate faces a different direction from the one below it, alternating somewhat north or south, so that attackers must fight on a fresh front at each successive gate. Each level sits roughly 100 feet above the one below.
Alan Lee, John Howe, Jef Murray, and Ted Nasmith have all produced paintings of Minas Tirith. Christopher Tuthill, writing in A Companion to J. R. R. Tolkien, judges Nasmith's Gandalf Rides to Minas Tirith the most fully rendered and realistic-looking, with a wholly convincing city in the background.