In reply to Mad_Ratel :
Assuming you want to buy for a bomber or challenge car. If you want to restore one, dont, no need when the best ones barely command $15k.... buy one for $15k and keep another $15-20k in your pocket.
So, what would I look at...?
Rust.
Rusty sills or sills that look like they are covered in filler.
Have a look under the sill at what is known as the "castle rail" it rust mostly towards the front of the car. From the inside, look about where your left foot toes reside towards the very front of the inner sill. It might be covered in a rubber matt or carpet, but it is a vulnerable spot. Rust that you can see is 10 times worse inside.
Here is a cross section of the sills showing how it all goes together as a dual box system comprised of 4 parts. The castellated bit should be an outie not an inny as I was drawing from memory at the time.
There should be a seam in the rocker panel at the front and rear of the door.
The "Dogleg" is the area just behind the door on the rocker panels. The inner sill lies about 1/8" just inside the layer of outer metal so moisture has a hard time drying out of this space and gunk accumulates. Few MGBs have not had surgery in this area.
The dogleg has been cut off and you can see the outer sill that lies under the rear quarter panel. Spring mount is just inboard of this location.
If the sills have some minor holes but seem more solid than not, you could drive the car for another 20 years before you really had to do anything about it; these are way overbuilt
Where the rear springs attach to the body on each end.
Floors of course, but they are easy to fix or replace. Just flat steel and 500 spotwleds to replace.
If seats are trashed, Miata seats are an easy conversion and much better.
Wiring is not the horror story that legend make it out to be. If it is haked to death, an $80 hot rod harness will solve all issues and do a better job.
Buy it if it is not scary rusty you really wont be risking much as long as wife unit approves.
Pete