How can I build the wyoming like montmorillonite unit cell in avogadro for a molecular dynamics simulation?
I would suggest you try and find the unit cell (.cif file) of the compound in question from the CCDC database, and then use Mercury (a free version is available at the CCDC website) to create the system.
You can of course use Avogadro if that is what you like, but in my experience the coordinate files it produces for super cells are quite messy.