Cost of replacing skylights in a small full bath

[Peter Morgan]

Hi,

After my previous tenants vacated the apartment,  I noticed the woodframe beneath the skylights turned moldy.

The tenant was not doing a good job with the exhaustion inside the bathroom especially last few months when they brought in additional members, the constant steam lingering inside the bathroom caused this issue. I will not be withholding any security deposit for this issue but would like to know how much can it cost to replace skylights or at least the wood beneath in a small full size bathroom. Also I would like to know if I can use any other synthetic water resistant material as a frame beneath instead of wooden frame. Appreciate your inputs on this. 

Thanks