Yes they should have to help rebuild the church they burned down. In doing so they can learn about the effort needed to construct a structure and the effort that is needed to do so. This type of rehabilitation will help not only mend the wounds against the community but show that person can undo and become a constructive member of the community.
It seems like church arsonists would be punished well if they were forced to rebuild the church as part of their punishment. I think the only problem with this suggestion is in the details, how would we go about doing this? Will we pay one guard to watch him while he works? What happens if he runs after reaching the location? What if he ends up harming other people who are working to rebuild the church?
I think these questions probably elude to the reason we don't do this in America. I think we should make a better effort to punish people in appropriate manners and the suggestion certainly seems appropriate, but there's no good way to implement those punishments.
If a person is capable of burning a church down, I don't think requiring them to help rebuild it will really have much of an impact on them. I think someone convicted of church arson needs be required to attend church services for a period of time. They should also be required to work at the church once it has been rebuilt.
I understand why the punishment makes sense, but I don't feel it is appropriate considering the perpetrator may actually get some sense of joy out of seeing their destruction first hand. I think they should owe money to help rebuild, but physically helping to rebuild would put a lot of liability on those watching the inmate and making sure they aren't doing more damage.