I've shared masses of writing with my T and she reads it in her own time without extra charge. I'm not sure if this is common though. A former T would read some stuff but always making clear that she'd only read it when she had time and not necessarily by the next session. Another T refused to read anything. It very much depends on the T. It would be absolutely fine to ask him what his policy is. I hope he is open to it because writing/creativity can say so much that talking can't.