I know exactly how to do that, having just finished creating a disk for myself.
First you will need to download, from the App store, Lion (again). It gets deleted once you do the install.
To download it again, go to the App Store and select Purchased. This should show you Lion as being installed.
Now click on one of the other sections, Featured for example, then hold down the option key and click the Purchased section again. It should show Lion with Install instead of Installed. It is finicky and may take a few tries to make it work.
Once you get it to work, download it.
Find the downloaded file, and right click it and choose "Show Package Contents". Navigate your way to "Shared Support" and find InstallESD.dmg
Drag it to the desktop, it will make an alias
Launch Disk Utility, put a blank DVD in your burner and then click the Burn button at the top left.
You will be prompted for the location of the file to be burned. Navigate to the Desktop and choose the InstallESD.dmg file.
Follow the rest of the prompts and at the end of the session, you will have a fully bootable DVD of Lion
I installed OS Lion and I want to create a boot up disk only for OS Lion in case if anything goes wrong later and I checked online, but its all before the installation. Any idea how to create boot up disk after OS Lion installation? Thanks a lot.