conservatory roof options

[gaz_moose]

The roof, windows and doors on my current conservatory are knackered so i was going to replace them before the winter gets here. i was looking at these warm roof type options that people fit these days. the fake plastic roof tiles look abit rubbish so i was considering EPDM as the dimensions are 2.8m x 4m so it shouldn't be too difficult or heavy to lay.

 

something like this.

 

it seems half the battle to make them not look stupid is to keep the whole roof structure as thin as possible.

id considered using a 44x145 c16 joist and then doing it as a cold roof with 100m celotex which would give me a 45mm air gap and a U value of 0.2.

 

but then i see people doing them like this

 

with the insulation pressed up against the OSB roof sheeting which confuses me as i thought the air gap should be between the insulation and the OSB.

I know the real answer is to knock the whole thing down and build an extension but it wont add any real value to the property and i don't want to spend the money🙄. 

what would be the best (thinnest) roof option to go for?