Shed wall/roof/floor construction- insulation?

[ABCwarrior]

Bit confused over insulation- planning a new self built shed, walls will be 2x4's, pent roof with corrugated sheeting, and I'd like it all insulated including the floor.
The floor will be a box section frame 2x8's, sitting on sleepers on slab pads and will have a thin (9mm)OSB underside with mineral wool inside and 18mm OSB floor.
The walls will be 2x4's- now, planning to use 12mm OSB on the inside again with celotex type stuff between studs.
So- do I need to put the VCL on the outside of the studs and then put on the OSB 12mm on the outside? I plan it to be sheeted in 8x4 (painted)OSB externally with "fake" vertical strips to go with the ones covering the joins?
For the roof on say a 15 degree fall could I do it in 2x4's with 12mm osb on the underside(ceiling), some mineral wool in the space, 18mm osb on the outside covered in a VCL and say 50mm of Celotex with the metal roof sheeting placed on this and nailed through the celotex/VCL to the timber or is just self defeating? Or would it be better to forget the celotex on the roof and nail some strapping on the roof and nail the sheets to that?Again it breaches the VCL but would it matter?

If anyone can post a link to any good sites would appreciate that?

Cheers

 

[hotrod]

How are you going to be heating the 'shed'?

 

[big-all]

you don't need anything bigger than 3x2" if you have support [a brick or similar] every 600mm /2ft
underfloor insulation is less crucial as you in general have still air protected by the building so less crucial to heat loss

 

[ABCwarrior]

It would be heated electrically with an oil filled radiator. I say shed, it may be anything up to 3mx9m and a workshop, depending how it works out cost wise and may have a wood burning stove put in at a later date.
Just want something quick and easy that won't boil me in the summer or be a waste of money heating in the winter.
Any tips on doing this as cheap as possible too would be handy???!

 

[big-all]

if you can gtee it will be water tight then loft insulation if not you need a breathable builders membrane then an air gap then your insulation then the inside panels [12mm ply in my case

i have pressure treated txg shiplap with 4 coats off sadlon had been 100% dry for 3 or 4 years so 2 or 3 years ago put 4"loft insulation in the 3" gap no air space then 12mm ply on the walls and 6mm on the roof no sign off damp touch wood
if i do get any signs off damp i will unscrew the inside panel if possible or cut a 4" vent and use the bosch 10.8v camera i am soon to get lol