How many marketing pages will you need?
ie. how it works, contact us, team, about, press, terms, FAQ, hiring
What type of site do you need?
based on your needs it might be business card website, landing page or website.
Do people have to log in?
An email login is generally best to start with unless your app will have tight integration
with services like Facebook or Twitter, in which case social login is better.
Do people create personal profiles?
A profile means that some of the people that use your app will have to enter information about themselves that might be viewed publicly.
Will you need to accept payments?
Accept credit cards, PayPal, Bitcoin.
Do people rate or review things?
People leave reviews and/or rate things.
Does your website need to connect with another app or website
(ie. share data with a mobile application)?
This means you'll need to make an API (or Application Programming Interface). It's how all your friendly apps talk to each other.
Does your website need search?
The cost to build a search function can vary greatly. The price given here is an average for search integration based on basic tagging. Not Google.
Do you need a Content Management System (CMS)?
A CMS will let you update content on your site without writing code (i.e. a blog).