Raid array configuration for large file server

We would like someone who has detailed and expert knowledge with setting up large raid arrays for a large file server. The server will be running nginx. We have have 1 server with 12x3tb drives. We are considering having this setup in a raid 6 array. Or may be a raid 10 array. The server will be having mostly reads, but about 10% writes, files sizes vary but on average will be around 300mb per file. Please let us know the full cost of setting this server up for optimal results. If you consider having a hot-swap drive a good idea on such a set up then let us know. thanks.