Who's in view?
Based on 1 Cor 3:9-15(the preceding verses) God's temple is the church. In particular, v. 9 says that "You are God's field, God's building."
The idea is a logical continuation of Paul's thought from vv. 1-9. Paul is the "master builder" who laid the foundation v. 10. In v. 6, Paul says "I planted, Apollos watered...". Apollos is one who built on the foundation which had been laid by Paul (the foundation being Christ v. 11).
The immediate context shows that this passage is about the church and not about individuals.
Destroying God's Temple
John Gill says on 1 Cor. 3:12 that the wood, hay, and straw which will be tested by fire are not referring to heresies because if they were, the person building with that material would be condemned. V. 17, however, does seem to be speaking about false teachers (who don't merely build with substandard materials but rather actually destroy God's temple) because it says that God will destroy them.
Vv. 18ff are not an unrelated thought. The wisdom of this age is opposed to the wisdom of God. This section of chapter 3 seems to be referring back to the apparent foolishness of preaching "the word of the cross" in 1 Cor 1:18ff. In fact, 1 Cor. 1:19 says that God "will destroy the wisdom of the wise". Paul is quoting from Isaiah 29:14. He doesn't use the same future verb Ἀπολῶ (fr. 1:19) in 3:17 (φθερεῖ), but their meanings are very similar.
Based on the similarity of these words and the connectedness of the thoughts in chapters 1-3, the destroyer of the temple of God is one who is wise in the world's sight and thus one who does not preach the foolishness of Christ crucified (and also raised--Paul is speaking synecdochally which is made clear in chapter 15).
The Reward
##The Reward## TheThe reward in view is the reward of the pastor seeing believers being truly edified as they are founded upon Christ. This can be seen from 1 Cor 3:8. The wages or reward in view is seeing believers being so built up in Christ that they appear as precious stones or gold and silver. It is possible for a teacher to be saved and yet teach in such a fashion that their followers are not saved. Paul is warning against this in verse 15. His instructions on preaching are necessarily in view.