I wish I could help but seriously thats like asking me to try and guess your favorite color.
Its not much point me suggesting you create a website about auto repair or gardening if you dont know anything about auto repair or gardening, let alone have a passion for it, so whats your passion, sport? books? gem collecting? look inside yourself, dont ask what is missing... ask what can I contribute, what do I know about.. and build a website about that.
Are you good at building websites? write about building websites, got a favorite game? write a walkthru, got a disability? write about living with that...the fact is whatever you write about there will be people interested.
Dont think about it, feel it.