Create custom region in a theme in Drupal 7 is very easy. Just follow the below steps.
Go to your theme folder, usually, sites/all/yourtheme/yourtheme.info, open the file. If the regions are not existing in your theme, you have to add yours. Suppose you want to add three regions 1) Header 2) Sidebar 3) Footer
regions[header] = Header
regions[sidebar] = Sidebar
regions[footer] = Footer
Open your template file page.tpl.php, located in sites/all/yourtheme/templates
<?php if ($page['header']): ?>
<?php if ($page['sidebar']): ?>
<?php if ($page['footer']): ?>
Clear your cache. Then go to Structure->Blocks . You can see your blocks coming in the region dropdown. That’s it.