Hi, im new here but have just started building with NBG. I've also found the sales staff a bit lacking but you can get that anywhere as we hunted around a bit before finding a house design that we liked (Hampton 19e) The builder we have been assigned is fantastic but the process has been very slow going, The staff at NBG hq are very young and so are inexperienced having never built a home before and having a general lack of life experience. Now this might sound a bit negative about them in general but they do use higher quality components in their houses that other companies only have as upgrades so in the long run you should'nt have problems with locks failing, tiles breaking etc. It will take a while to get the plans done as they only have one person doing them who may be young as well. (I am an engineer and i used drafting terms which an architect should know like the back of their hand but this person had a heap of trouble with)
Other things that hold plans up are the need for 5 star ratings which are done by a seperate entity and this can take a while as things may have to be changed like windows moved made smaller, double glazed etc.
I do recommend upgrading to double glazing which cuts down on noise and makes a massive difference to heating / cooling transfer. NBG have solar hot water as standard so also adding a 2100 lt water tank on top of the glazing will get your 5 star easily. (and you'll have a much better home in the process)
The main frustrating hold up you will have is the town planning and builders permits. The town planning has to be done first and all councils are hideously incompenent at doing any of it. If you knew how bad they are it would put you off building all together. We coped someone how didn't look at it for two weeks (it sat in her in tray) then she asked for stupid information that she already had and some of the questions she asked were items that were already set in stone by them in the first place. Then we were told two more weeks to do it. After hearing nothing i rang up and found out she'd left and it was waiting to be given to someone else. It was assigned i was told one week waited for an answer and was told this person was on holidays and someone else now was handling it and they reckon the end of Jan. And after this joke of an effort will come the building permit handled by an equally incompentent group. Now you might think that my house application has some sort of problem, but being an engineer i went through all the rules and regulations as well as the convenent and made sure the house applies to everything down to the last detail. Not to mention the houses that have already been approved in this area contrevene new victorian residential laws, the special council overlay for the area and the special conditions on the convenent haven't been enforced.
Most building companies have a special section for dealing with these council twits but NBG dos'nt which does mean you get hold ups thats not really their fault. Yes, It could be solved by them doing it in the hq with a special team instead of the contractors having to deal with it.
Overall though, im still quite happy with NBG so far, i have had a look at the builder's previous work and he is easy to deal with.
All companies have their bad builders they are stuck with because of the massive amount of new homes currently being built at the moment. My sister built two homes through porter davis with no problems but my parents who built a two story from their "premium" line have had incredible dramas, the door locks have failed and been replaced, 2 of the sink mixers had to be repaired as they leaked, and the roof leaks like a sieve! In heavy rain water gets in from the front travels down to the back of garage and runs down the wall, the front living room leaks and has holes that have appeared in the roof and water leaks down the back of the porch dangerously close to the light fitting. (they used the wrong flashing) The premium upgraded tiles all came damaged and were used anyway and those that broke after being fitted were not replaced just left there broken. But 99% of people who have built with porter davis love them.

Overall I feel that NBG do build great houses, if you check their specs against others you will see that the basic compenents, locks, sinks, taps, handles paint are all better quality than anyone else. Also their quotes for extras, like extra works to the slab (always needed with any house as blocks are never perfect) retaining walls etc were'nt inflated (Most companies inflate these prices to compensate for offering a slightly lower priced house) Its just that their HQ staff needed to have better picked., experience over cost. and no i do not work for NBG or have any affilation with them other than having a house built.
Whats really needed is a guide explaining the building process, as not many people understand it and so many people come unstuck at the colour appointments.