The following technologies would be needed build a dyson sphere: Technology to hold an atmosphere to its inner (sun) facing surface. This is if you want to live on that surface and not inside the spheres structure. Technology to co-ordinate the millions or billions of people required to construct such a sphere. An effective space engine (long lasting) and enough fuel to power the fleet of ships required. Mining, refining and manufacturing capacity in a space environment (the earth wouldn't have enough space or useable materials) and on the scale needed. The technology to live in such a sphere (life support, recycling etc). You would also need the technology to utilize the sphere to its potential which is that of collecting the entire power output of a sun. You would also need the technology to keep you on the sphere. This would require gravity generators or the sphere to spin. For a simple example a sphere with a distance from the sun the same as the orbit of the earth and an average total solid material thickness of 10 metres. You would need 2.8*10^18 cubic metres of material. The Earths volume is only 1.1*10^21 cubic metres. That's very roughly 1/400 of the earths volume in useable material for its construction.

You need to find a way to capture the ore deposits that are flung outward to the processing point in space! Otherwise you have to process the ore at the point of mining and then you still need to capture the finished material when the mass drivers fling it to your selected point of construction! Is this going to be like Babylon 5? Will the spheres be independent of Earth politically?

Actually, we have the technology to do it right now. It would take a ridiculous amount of time though. Also, the biggest problem to overcome is where to get resources to build it with. And manpower.