How DIYist are you trying to do? Is the goal something personal style that suit you or budget? Also what level of skills do you have in regards to metal works? I'm asking because there are options and people will direct you to good sources depending on what route you want to take. If budget build is the goal, you can do a Lone Wolf/XOP seat platform in the $50-60 range. OR I would promote my build which is around $100, a DIY LWCG Ambush.
SloMo has some great built if you want to check his YouTube.
Seat from Hawk Hang-on make good budget platforms too, just a little heavy.
But honestly for a new comer, I say get a Trophyline Mission or one of the platform from the classified, they have great resale value.