if else in wp php

<?php if( is_page_template('right-sidebar.php') ) { // check for page template
    $layout_classes = 'col-lg-7 col-md-12';
} elseif( is_single() || is_page() ) { // it's not the page template. Is it at least a post or page?
    $layout_classes = 'col-lg-8 col-lg-offset-2';
} else { // I suspect you want a fallback condition, not sure what it is.
    $layout_classes = '{something}';
} ?>

<div class="col-lg-12">
    <div class="row">
        <div class="<?php echo $layout_classes; ?>">