MdB said:.......[*]Main "A" frames supporting the roof only having 50x75mm cross pieces to stop spreading...........
You've got an absolute catalogue of nightmares there, but this isn't necessarily one of them. A tie beam is in tension: you could do the same job with a piece of fencing wire*. Obviously, one would need to see the particular case to be able to comment directly.
*There is a famous cathedral in Venice which uses chains, hidden inside wooden boxes. The span must be 15 to 20 metres, from memory.