i need to replace my garage roof,its a sectional concrete garage,whats the best/cheapest way,ply boards and felt or corrugated plastic/steel?

If the place is safe & you're not worried about heat i'd look at the clear plastic to give extra light.

osb bitchumen coated cheep and 100% waterproof then felt it if pitched.
(is it pitched or flat????)

its flat,couple of degrees of slope to the back of said garage.
i was told clear plastic wouldnt be strong enough when i built the garage,mainly cement type stuff and a few clear sheets

I made trusses for mine out of 75x50 off saw. That's 3x2 in real money.
I then sheeted it in 13mm OSB or sterling board.
Finally, a layer of green mineral felt.

It's what you could call a proper roof. A wee bit of work, but absolutely solid as a rock and gives me a bit of storage up there too.
There can't be any more than about 75-80 quid in that roof plus my time, but I defy anyone to specify a better roof unless they actually tile the thing.

I'd go over the existing roof with metal cladding like they do the sides of buildings with... with some insulation imbetween.

That way you don't have to dispose of the old roof (as everybody will think its asbestos!)
Its got 2 layers of waterprofing
And it will be warmer inside becase of the insualtion.

Thats what we did with a guy at works and he said its the best thing he's ever done after emptying buckets everytime its raid for the last 5 years!.

cheers for the input peeps,its off to the roofers today then