We are pretty lucky with the canal boat market in that as the majority of shells are steel, we only need to worry about the insides.
As an overview to try and bring everything together:
Ballast can be metal or brick, see our section on Ballast
Sub floors are usually marine grade 18mm plywood to BS 1088.
Top flooring surfaces can be whatever your preference is, all surfaces have been used in canal boats from laminate to carpet.
Side panelling is usually timber. 9mm veneer faced ply is a good compromise on strength and weight. Your builder may use different. Take his advise.
Specialist laminators can supply board in a huge range of surface finished from natural timber veneers through high pressure laminates and even leather. Modern techniques available to the trade means that almost anything is possible when considering internal finishes.
Work surfaces can be made from timber, granite and synthetic stone to give a variety of finishes.
Stainless steel tambour doors are available for a different look in the galley and to maximise cupboard space.
A look through an on-line fittings suppliers catalogue can provide hours of fun choosing cupboard handles.
Hidden catches and soft close hinges allow the cabinet maker to show off his art.
Bathrooms are one area to benefit significantly in recent years from the availability of new materials to the leisure market. Lightweight decorative panels adorn showers with a variety of surface finishes. Glass inlaid tiles and modern looking toilet systems provide a real home from home for modern boat owners.
Some traditional materials will be around for a long time yet though. Brass screws and fittings still prove to be the best at resisting corrosion through condensation and humidity. Despite being hidden behind wooden plugs, the best builders continue prefer to use these traditional materials.