I've bought some tickets.
Someone has done the maths, as far as is possible, and you've a better chance of winning an Omaze house (roughly 1 in 2,350,000 for a £10 entry, i.e. 15 tickets, and 1 in 1,175,000 for a £20 entry, 30 tickets) than of winning the National Lottery Jackpot (1 in 45 million, admittedly for a smaller stake).
Obviously an Omaze house is worth far less than the Lotto jackpot, but the odds of winning are much better.