Vertical blinds tend to give you the best option from a flexible point of view to an affordable one as well. Although Perfect Fit, Venetian, or Roller blinds would also be an option. As far as the roof space is concerned Pleated blinds are more suited to the slopes and angles which makes up the roof.
Another option to consider is our tinted window film in conservatories this method reduces the amount of heat reaching the inside.
If the roof is made of corrugated plastic a heat reducing paint can be applied on the outside surface.