For me a big book is a book with more than 400 pages.  I also read bigger ones sometimes, but I want to put less pressure on me. And I would be happy to tackle one book a month from my tbr. 
But make your own rules, however this challenge works best for you.

Please check also out the other reading challenges I am hosting. Some I'll set up later in the year, when readathons on booktube come up, for which none of the hosts do challenges on here.

If you have any questions, you can find me on IG as amelia7reads.