Strongly recommend NOT mining Siacoin.

The difficulty is very high for a coin with low value. You will get more profit mining something like Zcash, LBRY or even just using Nicehash.

If you have AMD cards like the RX470/480, you can dual mine SC with Ethereum with no penalty to ETH hashrate (so it's a no brainer). If you are using NVIDIA, do not mine Siacoin, or you can if you are happy earning less money. You'll make more on NVIDIA mining other coins (or using Nicehash) and then converting it to SC.

I have a dedicated mining rig with 6x1080 Ti, I mined SC for about a week until the difficulty spiked too much. Now mining SC is a total waste of my GPU power unfortunately.