It's simple to create custom csv in magento . follow the steps to create custom csv.

Create a controller to access data that you want to export in csv file like as below:

   
public function createcsvAction(){ 
        $param     = $this->getRequest()->getPost();
          $csv = '';
                $_columns = array(
                    "Shop Number",
                    "Shop Name",
                    "Total Sales ",
                    "Orders Sum" ,
                    "Orders Average ",
                    "Total Year To Date Sales ",
                    "Year To Date Orders Sum" ,
                    "Year To Date Orders Average"

         );
            $data = array();
            // prepare CSV header...
            foreach ($_columns as $column) {
                $data[] = '"'.$column.'"';
            }
            $csv .= implode(',', $data)."\n";
                    $data = array();
                    $data[] = $param['shopno'];
                    $data[] = $param['shopname'];
                    $data[] = $param['totalsale'];
                    $data[] = $param['ordersum'];
                    $data[] = $param['orderavg'];
                    $data[] = $param['yearsale'];
                    $data[] = $param['yeartotalsum'];
                    $data[] = $param['yearavg'];
                    //...
                    $csv .= implode(',', $data)."\n";
                    //now $csv varaible has csv data as string
        $this->_redirect('*/*/');
        $this->_prepareDownloadResponse('Export_sales_report.csv', $csv, 'text/csv'); 
     }