Organic (wood, cork, bamboo, etc) flooring materials will adapt to gentle undulations, and a more lumpy surface can be evened out by laying plywood first. The rougher the surface, the thicker the plywood needs to be, so this can cause issues with the bottoms of doors and etc.
A quick solution (even on 'suspended' floorplates) is to get a layer of 'self-levelling' concrete or sand & cement 'screed' laid over the top; this will automatically settle out (within hours) to a perfect level. However, this can also cause issues if the doors, skirtings etc. have been fitted slightly out-of-level.
A new-build house always comes with a guarantee, usually overseen by the National House Building Council. Most speculative housebuilders belong to this organisation (like a trade association, rather than an authority), and if you are not satisfied with the results when you complain to your builder, you can take your complaint to the NHBC.
If your housebuilder does not belong to the NHBC, they are still obliged (like any trader) to supply a 'fit for purpose' product. Reasonably level floors (argument might arise about exactly what is reasonable) are a requirement of the Building Regulations, and a house built without these is not legal, and may be uninsurable. You can involve the Local Authority's 'building control' department, and their Trading Standards office, if there are questions as to whether a new home complies with the building regulations.
If you are in the USA, then the official bodies involved will be slightly different, but it would be surprising if your state does not operate a similar system. Your housebuilder will probably (sometimes MUST) belong to an association that oversees quality issues, and the state government will have an authority who can prosecute sloppy (potentially dangerous) builders.