My water well shed is bad, I just found out how bad. What would be your best suggestion for dealing with this? One person says to just cut the bad spots and then cut something to overlay. I have limited experience on the table saw so these angles might be wrong if I try to make a new one. What should I do in this situation?

 

You have enough of the old left to act as a template. I'd hold a new piece of wood next to it making sure the tops and bottoms are parallel. Then scribe down the old rafter with a pencil onto the new wood. Then use a straight edge to extend the line all the way down to a point. Then you can cut it with any saw you have.

If you don't want to replace the whole rafter you can just get a piece of wood a couple feet long and do the same to mark the angle onto it. Then you can sister it to the side of the old joist with your new one providing support where the end of the old one rotted out.

 

Far easier to cut it with a ciruler saw.
You'll just have to hold the blade guard out of the way when starting the cut so it does not jam.

 

Alright got those made but here is a 2nd problem. I'd rather not tear out all of these walls. Yes I want to replace the rot but I dont want to deal with 28 year rusted bolts either. I've sprayed them with a solution to loosen so I'll try tomorrow. But should I remove everything or can I slip by in some fashion?

 

I would replace it all. Since it's so close to ground level and obviously getting wet I'd like to use lumber rated for ground contact. If you are located near the coast lumber yards will stock 2x4 treated for ground contact almost everywhere else they will be a special order. Or, you can use 4x4 for your bottom plate. You'll need to drill and counter bore if you want to use the existing hold down bolts. Then on top of the 4x4 you can use regular treated 2x4 for the joists. It looks like you will have to notch for the water pipe if you go the 4x4 route though.

If you end up using regular treated 2x4 for your bottom plate and studs I'd consider adding some galvanized steel flashing around the perimeter on the outside to help keep water away. Have the flashing extend down over the concrete about an inch. Then you can side over the flashing to make it pretty.