This FAQ shares some best practices in regards to page layout when building your landing page in the Builder.
What is the recommended page width for a landing page created with the Builder?
We recommend building your desktop page in a width of 1440 pixels, which should work for most desktop and laptop screen sizes; this should prevent any additional side-scrolling or white space from appearing on your landing page. When building your page, ensure the box labelled 'Scale the page size automatically' on the 'Page' tab is checked—this will automatically adjust your page width for the device it is being viewed on once it is published.
Is there a recommended page length?
There is no Unbounce recommended page length. However, avoid adding too much content or sections on your landing page, as not to overwhelm your page visitors.
My page is too short, and I notice some grey space at the bottom; how do I fix this?
Are you testing your page on a large monitor? The grey bar will appear only in cases where the monitor size is disproportionate to the page.
Your page will appear as expected when viewing from a 13-inch screen or smaller.
Additional Resources
What Are Some Best Practices When Designing My Landing Page?