About £54m has already been spent but that figure could soon rise to £70m.
This is on top of the £52m paid for Cardiff Airport two years ago.
The purchases were criticised by the Conservatives due to public spending cuts but ministers said the investments are to create jobs and growth.
The projects taken on by the Welsh government over the past three years comprise:
An overall figure of at least £54m which could rise to around £70m if the decision is made to go ahead with Callaghan Square.
In relation to Cardiff, it has been widely acknowledged that there has been a shortage of the kind of high quality office space needed to attract inward investors to the city's enterprise zone designated for financial services companies.
But Welsh Conservative leader Andrew RT Davies said: "When capital budgets are being squeezed and hospitals and schools desperately need that capital money, I would suggest the government's role is to invest in capital spend in schools and hospitals and not to compete with the private sector in building office space.
"They should help facilitate the building of office space by creating planning permission and infrastructure improvements but not (be) actually owning and developing offices."
A Welsh government spokesman said: "We are targeting investment all across Wales and in areas that have traditionally had limited levels of private sector investment, such as Denbighshire, Conwy and mid Wales, in order to create jobs and growth.
"We continue to work with the private sector to identify gaps between supply and demand for economic investment and are not afraid to invest where we believe it can create jobs."
The amount of money spent by Welsh ministers to buy industrial sites, business parks and office blocks for economic development could reach £120m within months.