(This is a sub-post from Tutorial 11: Starting Your Own Blogger Template)
If you're a beginner in designing a template, I wouldn't advice you to build a template by writing the codes from scratch; the task is doable but will take you a longer time. So, you don't have to reinvent the wheel! The best way to go about this is by starting from something that's already out there. Choose something close to what you have in mind - for example, choose either a 2-column or 3-column template depending on what you want.
But, when you do this, I strongly urge you not to make the intention of tweaking the code just a little bit and then claiming that the final version is your own design. That is just plain WRONG and UNETHICAL. The starting template is just a starting point, an empty canvas if you will, for you to 'draw' your own template. Use the starting template with the intention that the only thing 'useful' to you are just the Body section (which sets the overall layout and the number of columns), the container titles in CSS code (e.g. #main-wrapper, .sidebar, #sidebar2, .blog-pager, etc), and some 'default' codes that should not be tampered with.
When you're selecting the initial template, I'd advice you to choose a relatively simple template to help you go through the design process easily. If you're not sure which template to start with, you can always use my Generic Blogger Template, a basic 3-column template. If you want to use a 2-column template, read my Tutorial 10 to know how to modify the template into a 2-column template or change the sidebar location.