Rafter size and spacing

Hi how’s you To be rite you would be better getting a engineer to call out in a few min he will tell you how to do it rite this shouldn’t cost more than £200/300 . It’s ok to give you a timber size but it depends on the walls the roof is resting on if they can take the push of a tile roof , to add supports to the middle that would depend on what there sitting on you could end up transferring the load onto walls that can’t hold it , if any off these things are not rite the roof won’t be safe and all your money would be wasted a few hundred spent on a engineer before you start would be the safest cheapest why to get a new roof

5"/1,1/2" rafters spaced at 400mm , doubled up for velux(if any), and a small collar at the ceiling would be plenty of support

Six by four at 400 cc nine by three at 600 cc

Get structural engineer involved he will be able to first tell you if it can be done re loading on walls etc if it can he'll tell you all you need to know saving you time and money