With the recent advent of Starman over to asteroid belt, although he does have enough tools to achieve the purpose :) Do the asteroid belt have enough raw material to build a huge ring of solar panel that could power a human base at Ceres the dwarf planet? There could also be enough minerals and chemicals which could provide supply of oxygen and other raw materials on asteroids in general. What could be the possibility of that in near future?
If we consider carbonaceous chondrite asteroids, silicon is 9-15% by weight. Oxygen is 35-46%. So one ton of asteroid material would give about 100 kg silicon to make solar collectors, which in terms of a $t=$1 mm thickness would be $m/\rho t=$ 42.92 m$^2$. So if you get a one kilometre diameter spherical asteroid it would have enough silicon for 22,000 square kilometres of solar collectors if I did the math right. Even at a low efficiency that is going to be more energy than a modest Ceres base needs. And you would have a lot of oxygen.
Still, this is nothing close to a Dyson sphere. Looking at the light statite form of a Dyson sphere: the total mass of a 1 AU statite sphere would be 4.2184e20 kg, about 44% of the mass of Ceres, or slightly less than the sum of Pallas and Vesta. A lighter, purely absorbing statite shell would weigh half as much. The material demands can obviously be reduced by using a smaller radius.
Dyson's original paper looked at the total mass available in the solar system, finding that for a 1 AU sphere there would be enough for several hundred kg per square meter. More realistically, the asteroid belt has 3e21 kg of material. Spread across $4\pi$ AU$^2$ this is 10 g/m$^2$. This is more than enough to build a working Dyson sphere.