I've always asked myself this question too, and while browsing the internet I came across the right article.
In fact, it was said that researchers had collected a huge amount of information and images, taken from historical sources, regarding the materials , location and techniques with which they had been built.
The data was given to designers from which they created 3D images of the Seven Wonders.
So let's not waste time talking and go and see them:
1)The Colossus of Rhodes
The 35.5-meter Colossus once stood astride the Mandraki harbor. It was toppled by an earthquake just half a century later. It remained reclining, to the amazement of visitors, for another 800 years, until the Muslim caliph Muawiyah I melted the statue down and sold it for scrap.
2) The Pyramid of Cheops
Built over 4,500 years ago with stones weighing 2.5 to 15 tons each, the Great Pyramid remained the tallest man-made structure in the world for nearly four thousand years. Nearby excavations have revealed that up to 100,000 skilled and well-fed workers came from across the country to live in a temporary city while the pyramids in this region were being built.
3) The Hanging Gardens of Babylon
They're the only wonder on the list that could have been the product of an ancient writer's imagination. Native writers of Babylon which was located 80 kilometers south of what is now Baghdad, Iraq made no mention of the garden. But if it existed, it appears to have been a remarkable feat of engineering, with conduits carrying water up to 20 meters into the air.
4) The Lighthouse of Alexandria
This is the lighthouse from which all subsequent lighthouses took their cue. This structure, built by Sostratus of Cnidus, featured a blazing fire at the top. The building fell into ruin between the 12th century and the late 15th century, when the Mamluk sultan Qāʾit Bāy built a fort on the ruins of the lighthouse.
5) Mausoleum of Halicarnassus
The tomb built for Mausolus, ruler of Caria, an ancient region of Asia Minor, was so imposing that the late king's name became the generic term for large funerary monuments. Mausolus commissioned many large temples and secular buildings during his lifetime, and designed the Mausoleum himself.
6) Statue of Zeus at Olympia
This 12-meter gold and ivory statue was erected at the Temple of Zeus by the Greeks in an attempt to outdo the Athenians. Unfortunately, the frame and throne were made of wood.
7) Temple of Artemis in Ephesus
The building was built and destroyed three times. The first to demolish it was Herostratus, who burned it simply to gain fame. Then came the Goths, who destroyed the city as they passed through fleeing the Romans. Finally, a Christian mob razed it to the ground in 401 AD, leaving only the foundations and a single column which can still be seen today.