There's plenty. The vast majority of the 'shell' would be solar concentrators - basically aluminium foil or something like it. You can make a LOT of that by dismantling a few asteroids, never mind a planet or two.

Isaac Arthur's youtube channel goes into this in some depth (and is generally excellent, IMO). Here's an episode on Dyson Spheres:

https://www.youtube.com/watch?v=HlmKejRSVd8