you're going to be limited if you want a separate garage, what are your objections to an "open" floor plan? Quads take up a LOT of room unless you stand them up. You're probably looking at a 30' tag TH minimum with a garage big enough for two quads on their wheels.
The only ones I've seen with outside decks are pop ups and then the tongue weight has got to be very high.
What are you towing with?
DIRT BIKES RULE
'12 Duramax CC short bed
2019 Wildcat Maxx 285RKX