On button click you can do this:

 @api.multi 
 def view_report_button(self):    	
    return {'type': 'ir.actions.report.xml','report_name': 'your xml report name','report_type':"qweb-	pdf",'data': {dictionary of data goes here},}

Read more about custom qweb reports in odoo:

1. http://learnopenerp.blogspot.com/2016/09/how-to-create-custom-reports-in-odoo.html

2. http://learnopenerp.blogspot.com/2016/11/how-to-create-qweb-reports-in-openerp.html