Lamborghini's design boss Filippo Perini is doing a live rendering of the new Aventador Roadster. He talks as animatedly as he draws\: 'You always have to pay a big bill in terms of design when you do an open car,' he says, as the car's form magically comes to life. 'But on this car, we didn't kill its proportions - they're actually better.'He's right. Unencumbered by the need to provide any sort of utility whatsoever, Lamborghini has delivered fulsomely on the number one item on its job description\: design. The Aventador could have the dynamics of a supermarket shopping trolley with a wonky wheel and it probably wouldn't matter that much to its core audience. This is about seeing, and being seen in.With this in mind, Lambo opted for Miami's W Hotel rather than the Malmesbury Travelodge to showcase the Aventador Roadster. It's a location that supplies the sort of context a car like this lives or dies by, while rendering critical observations about understeer arguably superfluous (if you still want to know, though, more on that later).Not entirely coincidentally, Miami is a city squeaking at the seams with money. I counted seven Ferrari 458 Spiders, one Enzo and more Rolls-Royce Ghosts than you'd see in the factory car park.No Lamborghini is for the faint of heart or the shrunken of violet, but with the Aventador Roadster, Lamborghini clearly wants to reclaim the visual high ground from the Veyron Grand Sport. OK, so it's not a folding hard-top in the mould of the 458 Spider or McLaren 12C Spider, and the owner has to imperil his or her fingers physically popping out the panels, but, as Perini demonstrated, this has allowed his team to preserve the Aventador's incredible profile.The two-piece hard-top is made entirely of carbon fibre, so each panel weighs less than 3kg and could double as a decorative wall hanging.The simplicity of the roof nudges it ahead of the MurciÃ©lago Roadster's defiantly Heath Robinson affair, although the removal process is a bit unwieldy, and various bits of latch- and lever-pulling have to be done in exactly the right order lest you end up looking less-than-Miami-cool. You'll also have to pack minimally; the panels store away in a compartment in the nose, which done, space is at a premium. Perhaps a slender carbon-fibre toothbrush is available from one of Lambo's stores.Panels installed or stashed away, the Roadster looks even better than the Coupe, a deliriously complex work of industrial art. Inside, it's as insanely wonderful as ever, all jet-fighter nods and winks, with a start/stop button under a little flap, TFT instruments, and broad beams of leather. It's also extremely well made, and perhaps unexpectedly comfy.Of course, there's a chance you might actually want to drive the thing. There is a downside\: the Roadster's 0-100kph time is blunted slightly compared with the Coupe's, and needs a woeful 3.0 seconds rather than 2.9 to do the run. After that, it demolishes all the usual increments with hairy-chested nonchalance, and the top speed is the same at 350kph. At 1,625kg, the Roadster weighs 50kg more than the Coupe, and though its torsional rigidity is reduced, it's still very stiff.Needless to say, the Aventador's 6.5-litre, 691bhp V12 remains an absolute marvel, a hymn to furious, normally aspirated internal combustion in a world that's hell-bent on adding turbos and, worse still, electricity to the equation. Rumbling along the freeway, roof open, the Roadster is amazingly civilised, and normal conversation is no problem at 130kph. Tweaks to the spring rates and rebound damping mean that the Aventador's propensity to porpoise at motorway speeds has gone, and it's comfortable enough sailing along in Strada mode, even on the vast rubber fitted to our test car (355/25 ZR21s at the rear, 255/35 ZR20s up front). Both the Coupe and Roadster now get engine stop/start, and cylinder deactivation has also been introduced. This cuts emissions to 370g/km, and might nudge fuel economy up a smidge, but do you care?You need a track to really stretch that V12, and some time at Miami Speedway gives us the opportunity to tickle the V12's 8,500rpm red line. Unfortunately, circuit work also serves as a reminder that the Aventador is, um, not a natural athlete. It feels heavy and occasionally clumsy, and it will - here it comes - understeer if you get greedy on turn-in.Kill the stability control, and you have a clearer idea of what the chassis is really like. As you'd imagine from a huge car with a mid-mounted V12, you need your wits about you. The steering's great, but the car's throttle response is jumpy, and a satisfying sense of flow remains tantalisingly out of reach.But the biggest glitch remains the gearbox. Technical director Maurizio Reggiani admits that the software has been recalibrated to soften and smooth the action, but fast upshifts are still akin to a thuggish kick in the head. Unless Lamborghini can sort this out, they'd better get busy with a dual-clutch system, or risk a spell in supercar Siberia.Or maybe not. The Aventador Roadster is a head-spinningly cool thing, a modern masterpiece of product design and beautifully well made, too. It costs Rs 4.77 crore (ex-showroom, Delhi), and adds an extra layer of sensory overload to an experience that was hardly lacking in that department. Ridiculously, its price is arguably almost value for money in the absurd private jet/superyacht/Miami penthouse world a car like this lives in.The Aventador's power, pace and appearance inch it into the Veyron's mega-money realm. And while the 12C and 458 Spider are less expensive and more fun to drive, the Aventador Roadster gets round that by smashing your senses in every possible way.The numbers6498cc, V12, 4WD, 691bhp, 688Nm, 7.4kpl, 370g/km CO2, 0-100kph in 3.0secs, 350kph, 1625kgThe verdictRoofless Aventador is the best version yet of Lamborghini's V12 behemoth, and the perfect 50th anniversary birthday present from Lambo to itself.