Android app Splash Page

I have an existing website and an Android App. I want to have you create a splash page and code that we can have inserted into each page. The splash page should appear only when androids access any of the 10,000 pages of our website. This splash page will give them an option of purchasing the app or declining and going directly to website page they wanted. The page and function should look similar to the one used by westernunion.com. Access it by your phone before responding and then ask me any questions. Thank you.