All the texts for Genesis 1–11 [LXX] are now online. Please don't feel any obligation to start with Genesis 1 and progress through the text in order. If you'd like to work systematically through the text, feel free. But if you're more interested in the account of God's covenant with Noah than you are in Lamech's genealogy, skip to Genesis 9 and have fun.
One more thing: Soon I'll be putting together a list of common courtesies that GreekBible community members should follow. For now, let me just ask that if you're working on a text for which a translation has already been uploaded by someone else, please do not alter the earlier translation without explaining the reason for your improvement in that page's discussion forum (click discuss at the bottom of the page in question). Feel free, of course, to emend other people's translations; just be sure to justify the changes you make.
If you emend your own previous translation, it would still be nice for you to explain to everyone else why you felt your earlier work could be improved upon.