From britishmuseum.org:

Scientific dating techniques and painstaking archaeological research undertaken around the monument over the last few decades have brought the timeline of the site into focus. It is not possible to talk about 'one' Stonehenge – the monument was built, altered, and revered for over 1,500 years. That is equivalent to around 100 generations – it is worth pausing to let the sheer length of time sink in!

From Wikipedia:

There is little or no direct evidence revealing the construction techniques used by the Stonehenge builders. Over the years, various authors have suggested that supernatural or anachronistic methods were used, usually asserting that the stones were impossible to move otherwise due to their massive size. However, conventional techniques, using Neolithic technology as basic as shear legs, have been demonstrably effective at moving and placing stones of a similar size.[48] The most common theory of how prehistoric people moved megaliths has them creating a track of logs which the large stones were rolled along.[49] Another megalith transport theory involves the use of a type of sleigh running on a track greased with animal fat.[49] Such an experiment with a sleigh carrying a 40-ton slab of stone was successfully conducted near Stonehenge in 1995. A team of more than 100 workers managed to push and pull the slab along the 18-mile (29 km) journey from the Marlborough Downs.[49]

Each stone weights around 25 tons and I found this helicopter that can carry 33 tons: https://en.wikipedia.org/wiki/Sikorsky_CH-53E_Super_Stallion#Specifications_(CH-53E). So we could easily build this today. Probably wouldn't take long at all.