Brick on a roof

All Brickwork needs a good strong foundation to take load bearing , only lay on brick or block, never on shingles or tiles, remove shingles and wall plate back to Brickwork and build upwards, with lead flashing to roofworks.

Yes firstly a shingle roof would not support the weight of bricks or blocks and it would need to be on brick or block for the bond of the bed of cement

Yes, the shingle will provide no real foundation to have a brick laid ontop of it, I would strip the shingles back and lay brickwork off the original brickwork/blockwork/foundation

The can be yes

If any builder or bricklayer says they will build on top of shingles then I would be very wary of their competency and trade experience. Shingles are the roof covering that will protect the main roof from the elements such as wind, water, sun and snow etc.It isn't a solid base or foundation for building off. Hope that helps..

Yes shingle is not a base foundation and will create movement on the ground resulting in an u level and unsafe build!