The inner planets contain enough mass to create a shell of 1 AU radius with mass of 42 kg/m^2. That sounds like a plausible thickness and density for a sandwich of photovoltaics - GPUs - heat sinks.

You don't build a rigid shell of course, you build a swarm of free-floating satellites in a range of orbits.

See https://www.aleph.se/Nada/dysonFAQ.html#ENOUGH for numbers.