To actually update it, you would have to take it out and put in sheetrock.If you want sheetrock you can install it directly over the wood paneling.  1/4" thick sheetrock is available, which could probably be installed with construction adhesive to minimize the finishing work. 

@Mark Burik Think of putting a 8"x6"x2" thick wood on a mud area rather than 1"x6"x1" thick as your exterior, same principle.

It was literally over 1" thick.

scratch that.bank tore out mold infested carpeting and locked it in the shed. they also used thick paint directly over the mold on the drywall.

An overall thickness of 4mm would be my choice with a minimum of a 12 mil wearlayer combined with some type of scratch resistant coating like AO or ceramic bead.

What thickness of hardboard insulation are you using as well as your underlayment for your final roofing material when you end up re roofing?  

They are great nice thick books too, not some pamphlet that looked like a book online, very well made books.Any chance on a hardcopy in the future?

We are in the process that when each unit is vacated, we install carpet and a thick pad.

And yes, tell the tenants to run the ventilation fan during a shower, and recaulk using a good thick bead of 100% silicone sealant...but sadly, I think the problem is that the greenboard behind the tile is rotting out.

Leandro,EPDM roof is a better system although it has more pieces to it so if not installed properly it will leak- make sure they tear off old roofing down to the sheathing or plank and start fresh-ask your contractor what size of rubber roll he plans on using ( they come in a variety of lengths and width, the less seams the better) -the rubber rolls come in different thicknesses or mils 45 mil is a minimum - make sure it an fully adhered system where they are gluing the runner to the fiberboard - As long as they are using primer/glue/ seam tape on all your seams as well as some sort of decent termination bar at the roofing edges you should be fine -how’s you slope on the roof currently?