Suggested height of a cab.

Ok, I've never really seen a marijuana plant in real life so I have no idea how tall they get. If I plan on using MH for veg and HPS for flower I have to take that into consideration as well.

How tall should I build my cabinet, like 6 feet or so?

what are the dimensions of your closet? you can grow a plant 6 feet tall but that would take forever.

You'd never want a 6 foot plant indoors. It's not an efficient use of artificial light.
Plants grow as tall as you and their genetics let them. Most indoor growers will stay at about 3 feet and under.
A closet that is at least 6 feet tall will give you enough space for a 3 foot plant, a foot tall pot, and 2 feet to hang lights and ventilation. You will need to run an air-cooled hood with a large light in that space.
Pick strains that stay short and shrubby and train them so that they go into flower at less than 2 feet in height.

Ok yeah I didn't mean I wanted a six foot plant - I was just wondering how tall I should build it so I know I don't run out of space with lights, plants, etc.

Thanks everyone!