If you want to build a website, first think about what do you like, and go for it.
Go to Google Keyword Planner, enter your keyword, select your targeted location from the options.
Check how many searches the keyword has.
TIP: choose 2-3 big keywords, and 100+ secondary long tail keywords.
chrome or firefox extensions/addons.
Go to Google.com or your countries Google. Enter your keyword, but first make sure you have those two extensions/addons activated in your browser.
You want to see what are the top 10 results, how powerful are the domains and pages of those results.
If PA (Page Authority, according to moz/mozbar is lower than 40) you can go for that keyword. Do all of this with all your keywords, but first start with your 3 main keywords.
Also check how many backlinks a page has with seoquake, the age of the domain. and so on.
Hope this helps.