There is lots of information about building a tadpole trike available online besides what I have written myself. I am not really adding anything new here. Rather I am simply posting this one article with links to all that I have written about the subject before making it a bit easier to find it.
Here is one of them: https://tadpolerider2.wordpress.com/2015/01/30/gotta-do-your-homework/
Here is another one: https://tadpolerider2.wordpress.com/2014/05/11/tadpole-trike-construction-the-science-of-tadpole-trike-steering/
Here another one: https://tadpolerider2.wordpress.com/2014/05/11/home-built-recumbent-trike-detailed-plans-and-construction-steps/
And here are a bunch more postings on my blog about custom built trikes: https://tadpolerider2.wordpress.com/category/homemade-tadpole-trikes/