, i love the Dashboard. but it doesnt give any platform to developer to design their own theme..
You cannot build or use your own custom theme built from scratch at WordPress.com. The only themes we can use are those found here > Appearance > Themes
This is a multiuser blogging platform. All blogs wearing the same theme are using the same underlying template and we members cannot access the underlying files and edit templates or themes. http://en.support.wordpress.com/themes/editing-themes/
There are two free themes, Sandbox and Toolbox designed to allow maximum flexibility for CSS editing and creating new “skins”. Toolbox is more modern and includes a lot of support for CSS3 and HTML5, so it is really only limited by your skills and knowledge.
If you have CSS editing experience the upgrade will allow you to stylize the appearance of the WordPress.com themes you find here > Appearance > Themes, but will not allow you to change the functionality, by editing the underlying template. Please read this section > http://en.support.wordpress.com/custom-design/#frequently-asked-questions
Also note that CSS is theme specific, so you cannot use the CSS stylesheets from other themes with the themes at WordPress.COM. http://en.support.wordpress.com/custom-design/custom-css/
Does the Custom Design upgrade let me edit HTML?
No. The Custom Design upgrade allows you to edit fonts and CSS only. You can change the appearance of a theme, but not its HTML markup, PHP code, or content. http://en.support.wordpress.com/custom-design/#frequently-asked-questions