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You can never read too many books.
Literal
Books [topic-は] how-much read-[even-ても] read-too-much thing [topic-は] not-exist.
A double-framed structure. いくら~ても ('no matter how much you X') sets up an extreme — 'however much you read.' 読みすぎる事はない ('there's no such thing as reading too much') uses こと + はない to flatly deny that the extreme is problematic. The overall meaning is 'you can't overdo reading — read as much as you like.' A classic bibliophile aphorism.