Check my history for other variants/optional items of the Ra build, hard to fit it all in here with how flexible of a god he is. I'm playing it pretty often these days so the build might evolve at some point. Genuinely think he's one of the top ranked solo picks right now if you like playing him.
relic choice depends a lot on what you are vs, beads/shell are the best default buys though. Also T1 will be Shield or Rune based on laner.
Ra stacks Gavel really well when he starts grouping with the team. It's a really solid INT and HP boost. If you need both of those over the safety of Shell swap it out. I'd also buy Gavel earlier in the build, probably before or after book if I did this swap and shift the rest of the build accordingly.
Similar swap as Gavel, but E-Staff is especially strong if you want to shred a lot of HP off the enemy frontliners, whilst also gaining that HP for yourself.
Every shot of ra 2 does proc Phoenix still, but at a reduced rate. Still ends up being a lot of sustain if you want to all in that playstyle.