Wot is minimum pitch on Rosemary clay tile roof?

[mazears]

My kitchen was originally a pitched roof. In the past it's been changed to a partly flat roof (felted)and partly pitched using rosemary clay tiles. I'm keeping the headroom at kitchen end as best i can (the reason it was probably changed-the floor originally being lower but now all on the same level). I am also adding a velux window. I'm changing the roof back to a fully pitched using same tiles and was wondering - What is the minimum pitch i can use? Pretty sure the roof will have to go further up and step down into smaller roof (although would be great if i can keep all same level but surely the angle of kitchen roof would be too shallow?
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[Alastairreid]

minimum pitch for rosemary tiles is 35 degrees.

 

[mazears]

1. Is there any other tile i can use that closely matches the red rosemary tile, but which will allow for a lower angle pitch to possibly level up with the top of the other smaller roof?
2. If i used the original clay tiles and extended the kitchen roof upwards at 35 degree, does there need to be a gap between top edge of roof and bottom of the window - if so how much ( ie. for lead flashing etc)?
3. Is there a min degree also for the velux window?

 

[Alastairreid]

minimum pitch for a velux is 15 degrees.

the roof should be detailed to allow an upstand of 150mm on the lead apron