Design recomendations for Mosfet H-Bridge
I would suggest starting with a smaller H-bridge project first.  The control of MOSFETs seems simple, but there are some subtleties which can easily bite you if you are not careful.  When designing a smaller H-bridge project, it's not too hard to protect a circuit in such fashion that even if something goes horribly wrong it won't do much damage (and may very well not do any, though whatever caused the problem will need to be fixed in any case).  This is useful not only from the standpoint of reducing the amount of time spent replacing blown components, but also from the standpoint of being able to figure out what happened.  If something goes wrong in a 12V 30A H-bridge controller, it's likely to cause enough destruction quickly enough that it will be hard to analyze the pile of cinders and determine what failed first.

Beyond that, the reason companies make H-bridge controllers is that other companies buy them, and the reason that other companies buy them is that a surprising number of discrete components are required to safely and optimally control a MOSFET.  If one is trying to control a MOSFET whose Absolute Maximum Vgs is 15 volts, and an inductive transient causes Vgs to reach 30 volts even for a microsecond, the part may easily be destroyed (the voltage required to destroy the part would most likely be around 20 volts, but one shouldn't rely upon it being above 15.01).  Keeping Vgs below 15 volts may not sound hard, but factors like parasitic gate-drain capacitance can lead to some unpleasant surprises.