Engine valves are made from various materials and in some engines the valves are different materials for inlet and exhaust. Most valves are usually made from materials such as carbon steel alloy/s, stainless steel, titanium (performance), chromium (mixes). It depends on the engine and it's performance etc. There is a large amount of info on 'Google' about this.
Your shell thickness would almost certainly depend on what you are modelling I should think.
appreciate your response!
ill sure check with some engineers here regarding the elements that you offer.
If you have no idea about product you are going to design, particular wall thickness will not help with the project.