The LS3/5A cabinet is much harder to make from scratch than first meets the eye. Cabinet kits can be bought from Falcon Acoustics which certainly makes the job easier.
Peter Lotter has produced a set of drawings from his own DIY cabinet project and very kindly made them available here in pdf format for other constructors.
Peter Lotter’s Cabinet Drawings (pdf format) Please note that while Peter has taken every care to make these accurate, they are not official drawings and have been produced by measuring and calculating the dimensions from real LS3/5A cabinets. They are intended only a a guide for DIY constructors and neither Peter nor myself can be responsible for any losses incurred as a result of following them.