roof top in Melbourne??

Open Sky, whilst a Sydney based company, should be able to help.
Give Hans a ring and see what he can do for you.
I know you asked for Melbourne based, hope this will help.

www.opensky.com.au

Tel: (02) 9565 5345
Fax: (02) 9565 5346.

I have one of their EziAwn and am totally happy with it, best purchase I have made.

Aussie Taveller have an outlet in Camberfiled I think, check the phone book. We considered one of their's a while ago, they are quite good.

Simon Heard in Shepparton make them as well, but the quality of some of his canvas work is a bit suspect.

Georg, Although not Melbourne based, Shippshape make an excellent roof top camper in my biased opinion. They are an excellently made product, made in Australia, erect in under a minute when you've had a little practise and easy to pack up.
There is a link to them via the advertising section on this site. There made in Sydney and the guy is very helpful and ships them anywhere. Price is quite reasonable in my opinion.
Ventilation is great and although I'm about 185cm tall, I find it very comfortable.
Had it for over 12 months and spent 7 weeks in it last year up to the cape and back.Dare to Lead not to Follow