I have recently purchased a classic Cannondale CAAD 3 frame of ebay which I am looking to build up for my 11 year old son. The idea was/is to get the lightest bike possible to help him out on longer tided/climbing hills. It is a lovely frame which has disc brake mounts, but has the specific oversize headtube ….., so will I need original Cannondale forks? or is there any way I can get hold of some 1 1/8″ carbon folks and maybe use an adapter?

Any help will be hugely appreciated and any advice on cheapish lightweight components would be great.

yes – you can get reducers so you can use 1 1/8th forks – they appear regularly on ebay as do secondhand headshok which would probably be your lightest option for suspension.