A specification is a long document written to be skimmed. Six lines in it tell you almost everything about how the house will perform once you are living in it, and they are rarely the six lines the brochure highlights.
The six lines
- Wall and roof U-values — lower is better, and the roof number matters most.
- Glazing unit make-up, including the gas fill and the spacer material.
- Air-tightness test result, not the design target.
- Floor build-up, especially the acoustic layer between storeys.
- Structural timber grade and moisture content at install.
- Ventilation strategy, and whether it has heat recovery.
If a developer will not publish those six before you reserve, that is the answer to your question.