I am a new owner of a 1958 ranch in slab, fixer upper.  Except for the studs in the walls, and about 80% of the concrete slab, everything else is problematic. 

the house has beautiful beams, spaced 4 ft apart and a roof that is actively leaking in four spots. Roofing companies have backed out of doing the job, which needs to be a complete tear off to the beams. 

it was suggested that we either, 1) add rafters in between each beam to add support for actual plywood sheathing.  We were told the Beams are too far apart to support plywood on its own. 

or
2) install tongue n groove sheathing, poly iso board, then paper and shingles on top of that. 

Option one: 3K interior labor adding beams, about $3,600 in lumber, $5k spray foam insulation, $1k in drywall and paint that I will DIY.   Then the $10k for the new roof. 

Option two would preserve the beams, add tongue n groove interior ceiling as well as structure. And cost us a third the cost of the whole house. Quoted about $8K for tongue n groove, $10-15K polyiso board, 6-7 days labor for carpenter crew to install tongue and poly, at $7k then $10K for roofing company to do the roof. 

are these the only two options?  What do people do with these houses?  Are there anyways to do option 2) tongue n groove, for less than $40/$50K?

i think the polyiso board was about $160 per 4×8 and our roof is 38 square. If there was a more economical way to pull this off we would
 e going for option 2 as it preserves and enhances the mid century modern aesthetic of the house.