Bamboo is quite expensive but worth the effort. in building. .and cutting ( it will burn through your tools fyi). I went with honey bamboo Ply. bamboo ply is quite a bit thicker then other types of Ply also. I think the sheet sizes were 4x6 and about $100 (Canadian$ but bought from Seattle) a sheet.
One other thing to try if you have the space is to put a small void (mine was 2" by 6") in the middle of the plinth layers i put mine under the tone arm, it can not be where your going to machine out the area for the table or arm. I filled the void with clean dry sand then sealed it in the build up. this adds some damping. note you don't want too much or it deadens the sound but a little helps with resonance in the table - plinth.
One other thing to try if you have the space is to put a small void (mine was 2" by 6") in the middle of the plinth layers i put mine under the tone arm, it can not be where your going to machine out the area for the table or arm. I filled the void with clean dry sand then sealed it in the build up. this adds some damping. note you don't want too much or it deadens the sound but a little helps with resonance in the table - plinth.