Roof Insulation on the slope

I want to insulate my roof.  I would like to insulate the sloapy part of the roof because we use the roof space to store .... junk... and I would like to keep the junk cool.

Factors to consider

1. Dirt and crap seems to get into the roof space so insulation that relies on reflective properties will not work.
2. Cost
3. Ease of Installation 
4. I don't like fibreglass type insulation.
5. Needs to be installed on the sloapy part of the roof.
6. Insulation properties - These seem to be quantified by an R value.

Insulation Options

Fibreglass Batts
Personally dont like these as I am concerned about breathing in fibers.
They sit down on the ceiling and so of no use for keeping the ceiling space cool.

Polystyrene Foam
Bought 10 sheets 2400x1200x50.  $29+GST each so around $300.  I reckin I would need about 4x this to do the entire roof.
I have cut these up and I am shoving them between the roof trusses.
It is a lot of work.  I can see why this is not a commercial option.

Concertina Foil Batts
http://www.concertinafoilbatts.com/

KingSpan Air Cell
http://kingspaninsulation.com.au
? "must be supported on mesh"


Tropical Roof
Install a second layer of corrugated iron on top of the first with an air gap between  Or a whole stack of solar cells.

Paint the roof with something???

Foil Bubble Insulation
http://www.diytrade.com/china/pd/7020464/roof_insulation_material.html
and all over ebay