Google Display Network Size - HTML5 ads requirement
Adwords account should be: 1. Open for more than 90 days. 2. Ad spending USD 9,000 total lifetime spend.
If your site not match above requirement but insist to use HTML5 banner, you may click on this form
You may ask for Google help on that
Google Display Network Size - GIF banner spec
Supported ad sizes
Square and rectangle
200 × 200 Small square
240 × 400 Vertical rectangle
250 × 250 Square
250 × 360 Triple widescreen
300 × 250 Inline rectangle
336 × 280 Large rectangle
580 × 400 Netboard
Skyscraper
120 × 600 Skyscraper
160 × 600 Wide skyscraper
300 × 600 Half-page ad
300 × 1050 Portrait
Leaderboard
468 × 60 Banner
728 × 90 Leaderboard
930 × 180 Top banner
970 × 90 Large leaderboard
970 × 250 Billboard
980 × 120 Panorama
Mobile
300 × 50 Mobile banner
320 × 50 Mobile banner
320 × 100 Large mobile banner
Supported file size 150 KB or smaller, 3 times repeat of the GIF
Responsive Display Ad
Text: Short 25-character headline and a longer 90-character headline that will display when size allows. A 90-character description allows brands to control ad messaging.
Image: One large image and One logo square size