In the last year or so there has been a very real explosion of plastic kits available on the market, creating a boon for wargamers.
One of the first to the market (besides some plastic upgrade parts offered in Battlefront kits) is from Plastic Soldier Company. While these kits are simplified, they are nonetheless designed for wargamers, simple to construct, but still offering sufficient details for a good appearance.
The kit offers a whopping 4 different versions to construct: F1, F2, G, and H. While this is of obvious benefit to the modeler, unfortunately out of the box only one variant can be made accurately: the short-barreled F. To make any of the other variants, you will need to modify the kit parts in several ways. Most are easy to accomplish.
Panzer IVF2: This variant is a bit more challenging to build compared to the others, and requires additional materials to do it well. The primary problem is that the muzzle brake depicted in the kit is the incorrect type, being a double baffle type, when it should be a single baffle type. To make more accurate, remove the muzze brake and use a plastic bead as a replacement. When glued on, drill a single hole through the bead fro the side to produce the muzzle brake. You can also model a late version by removing the circular flare hatches from the driver's comparment hatches, and the vision hatches on the turret front-sides.
Panzer IVG: This is the second easiest build in the kit. Simply remove the left-hand vision hatch next to the main armament, the 2 vision hatches on the turret front-sides, and the flare hatches from the driver hatches. You can also model this tank with skirt armor, as some Gs (especially late) receive this upgrade.
Panzer IVH: This version is a bit more challenging than the G, but can be done in much the same way. Do all the modifications for the G, with the addition of a single-piece circular hatch hinged to the side (opens to the left, if you view the tank from the front). Although some of the early production Hs were bare, many received Zimmerit, and this is a real challenge to add to this kit. The manufacturer can't be faulted, as this would have made a kit with excessive parts, and thus made it much more expensive as well as challenging to build.