Let's start with the important stuff, how much performance has it lost compared to the coupe? Well the answer is not much, it still produces 710bhp and the top speed only 10mph slower (from 212 to 202mph) with the roof down. The 720s Spider is only 49kg heavier thanks to most the roff bits at the back being carbon fibre. 0-60 is exactly the same at 2.9 seconds and the top speed can actually be 212mph if you put the roof up.
The roof is rather amazing. The main roof panel can be a carbon fibre framed glazed panel to let more light into the cabin or at the push of a button it can become tinted, and then obviously you can fold the whole thing away. It takes only 11 seconds to fold away and you can do it at 31mph.
The aero has been reworked too. The buttresses have holes in them so the air isn't coming at them and having to create drag as it finds its way around it. It also has a slightly wider rear wing and the under aero has been totally reworked too so that less weight has to be added to stiffen and stabilise the car.