I'd be very wary about buying off plan, especially in the current climate. If you 'bought' now how much of a commitment is it to go through with the sale. If house prices have fallen by the time your house is built are you going to be ok with paying the price you've paid. If you're just reserving off plan that's slightly different.
Be aware of planning changes, all the new estates around here have at least 2 or 3 more planning applications after the original reserved matters normally relating to substituting plots or rejigging the layout. You won't be notified of these and it could impact on your plot.
Parking allocation looks good on paper, but often parking spaces are in rear courtyards and some distance away from your front door. This means people don't use them, parking is also less secure by virtue of it not being overlooked.
Storage wise we saw some houses that had loads of inbuilt storage and some that had none so really depends on the house. A lot of the larger houses we looked at were top heavy, decent sized bedrooms, bathrooms and ensuites but the space downstairs didn't match up with just a kitchen and lounge/diner.
Just noticed about the first time buyer Government deal, do your research very carefully. Most of these schemes served the interests of the housebuilders not the first time buyers. I think some are 'ok' but have heard of a lot of people getting their fingers burnt with these sorts of deals.