If you're not qualified to check the below, hire a professional, very cheap. There's no need to take any risks.
Ask to see architects drawings, detailing structural items.
Ask to see the local authority building permit.
Ask to see the individual land title plot for your house, ie: has the main Chanote been ‘cut’ yet, it takes two months so should be done before show house is even finished.
Actually read the conditions in the contract (I know I'm pushing you to the limit here

Check the footing’s go down at least 1.5m through established earth (ie: not newly built up earth), with at least a 1.2m square concrete padstone under the footing.
How long has the infill earth been left before they started building ?
Check they’re using 12mm dia reinforcing steelwork in the underground beam system and above ground columns, and not a smaller size (some only use 9mm or 10mm).
Check the underground beam layout from the architects drawings to make sure that all walls are built off these beams and not off in-filled concrete.
Check they are using '3-phase electrics' (not western 3-phase before anyone picks me up on that) with their own dedicated transformer, tapping into the higher located 11kv supply, rather than the lower single phase cables the whole area shares, which goes down often or is insufficient in certain areas.
Check they are installing an underground concrete drainage system going out of the project to the local drains or stream/river.
Check they are using concrete lintels above doors and windows and not just building bricks off the wood frames.
Check they are using grade ‘A’ cement.
Check they are using fine sand (more expensive) for the rendered walls, no plastering here. Run your hand over my breasts, err I mean walls to see how lumpy/rough their rendering is.
Check they are using quality pool equipment, or the like, and not cheap Asian equipment.
Check they are using steel traps, flexible hoses, valves and fittings in the bathrooms, rather than plastic ones where the joints blow after about a year.
Check they are putting electric cables in conduits.
Check they are using the latest regulation 3-pin sockets and that they are grounding them to earth, ask to see the earth rods in the ground outside.
Look at the plasterboard ceilings and see if you can see the joints, you shouldn’t be able too if they are quality tradesmen and ‘skim’ properly.
Check the tiling to see if the tiles are even or if any corners are jutting out, just run your hand across them.
Look at the swimming pool water line against the tiles to see how good/straight their tiling is.
Do they use compacting machines to ‘pack’ the earth down ? If not forget it.
Check they put concrete access roads in.
If you want to know if they can build walls straight look at the cut tiles along a run of wall.
Never buy off a Spurs fan or someone whose always down the pub. Doh!
There's probably loads more, why don't the proffessionals in the business, like Jaime etc, add to the list.
Burger