Looking on the internet deeply has found these results:

under construction is the most popular phrase on the web.

in construction 143,300,000 results on the web	under construction 166,000,000 results on the web More popular!
Some examples and use cases from the internet:	Some examples and use cases from the internet:
Ty has a career too, in construction. Montpellier high Project cost overruns and delays in construction So, this is just in construction, and there's a tensegrity structure. And this is Tully in construction now. speed rail link. Question 44 (Ignasi Guardans Camb�): Delay in construction of Perpignan More jobs in construction, security even.	Now it's more under construction. Parts of M.S. One are still under construction and need constant maintenance. Hundreds of others are under construction, with large scale excavations and landfills. This place was under construction when they hit the city. I think it's under construction now. Today, the Mediterranean region and Europe form a strategic and economic area under construction. I've linked Simon to a cellular jamming array currently under construction in Cuba.

in construction

143,300,000 results on the web

under construction

166,000,000 results on the web

More popular!

Now it's more under construction.
Parts of M.S. One are still under construction and need constant maintenance.
Hundreds of others are under construction, with large
scale excavations and landfills.
This place was under construction when they hit the city.
I think it's under construction now.
Today, the Mediterranean region and Europe form a strategic and economic area under construction.
I've linked Simon to a cellular jamming array currently under construction in Cuba.