Steel tie rods for rafters

Hi all

I am building an extension that is 4m wide internally. The rafters are 225mm thick and the ceiling will be pitched. I do not want to use exposed timber joists through the ceiling and would prefer to use steel tie rods instead. The room is 5.5m long. As the roof span is not large would two steel tie rods be sufficent for this space.

Any ideas wlecome

thanks

Recommend you employ the services of a structural engineer to advise and sign off on the detail it would help in the future if you ever want to sell. Last time I saw a similar detail the tie rods were only part of the structure, a reinforced band was formed and the wall plate bolted to the band. Also steel brackets from the rafter I think it was every third one to prevent the rafters from spreading on the secure wall plate.