You don't need new rafters unless the existing ones are rotted. If you don't go with metal, use a TPO roof and get a commercial roofer to do it. Residential roofers don't know what they are doing with flat roofs-at least in my area they don't. We just put a standing seam metal roof on our low slope mid-century house. Our slope is 2/12. You need special standing seams built for low slope. Do you know what the slope of your roof is? Honestly, your slope looks extremely low. If you can't see the roof, I wouldn't go to the expense of metal. Cute house, BTW!

Standing seam roofs are can be attractive, practical and very durable. Try searching Colorbond Steel products on Houzz for ideas.

Standing seam will give you a good, long term roof. It will also look 10 times better than a TPO roof. Residential wise, are there views of the roof surfaces from your lot or the street? Neighbor elevations with a clear view of your roof? Do you care what it looks like? Many of these roofs in the Pac SW were Built-Up with Decomp Granite or Sandstone (desert dwellers). The rock was decorative but also provided some color options. We just re-did a mid-century a while back with a nice rock roof, very light colored decomp granite, good reflectivity. These roofs are typically poorly insulated from this generation, so depending on your climate, you may want to address that with your re-roof as well.

We used to have a mid century modern house with a very slightly sloped roof. The original materials were tar paper, tar and little rocks. I liked the look and it worked well. It had never been redone, and the house was built in 1964. We did have to rake and kill moss every now and then. I don't know if anyone even does that type of roof anymore.

If you are going to keep the house looking pretty much the same without making big changes, then I would suggest keeping the roof as is and redoing it with a new "built-up roof" or using a newer "rubber membrane roof" designed for "low slope roofs" like yours.

If you want to make bigger changes to the house and change the slope of the roof, than I suggest that you hire an architect to help you modify the house into a design that works well and is beautiful..........you can have a beautiful remodel with a budget and a good architect will be able to work within your budget.....

We recently remodeled an older house that was somewhat similar to yours and we used some metal roofing and changed the mid- century modern with an odd second floor addition, to a coastal "island" house....

I have attached two finished photos and the last photo is the BEFORE PHOTO of the before house.....which reminds me of your house.......
Good luck with your house.......

even if you keep the roof and the appearance as is, it can be a very nice house............

WOW!!! I just found Houzz yesterday and am blown away! Thank all of you for your kindness in helping a complete stranger figure out what to do!!! Wonderful advice to consider!!! THANK YOU!!!