There is no simple 'right' answer to this.

A mould that must be stable and rigid eg. a wing will need more layup and external bracing than a canopy.

Moulds that SPLIT will need planning and usually benefit from the incorporation of a frame.

For a 40 inch long fuselage I used a 2" angle iron frame with welded corners on both sides with dowel bolts to ensure alignment and kept adding glasscloth till it was about 1/4 inch thick.

Here is a guide to producing a simple cowl mould. http://www.fibretechgb.co.uk/TipGlsFbrMld.htm


If you want to do something more complex a good library should provide a book The Glass-fibre Handbook by R. H Warring is a good starter.