EXCLUSIVE JUST LISTED SPONSOR UNIT ~ NO BOARD APPROVAL  Spacious 5-Bd. Townhouse Triplex w/ 2 Fireplaces, Huge Private Roof Terrace + Laundry Room  Looking for a co-op that feels like a private house with plenty of outdoor space? This large 5-bedroom, 4.5-bath townhouse is just the ticket! Plus, it's is a sponsor-owned unit that requires no co-op board approval.    Nestled along a tree-lined road at the edge Riverdale's of Estate Area, the townhouse boats three levels plus a huge private roof terrace (it's 22 by 42 ft.) for lounging, planters and outdoor entertaining.    It is splendidly situated at Dogwood Close, a lovely and leafy garden-apartment-style complex surrounding a landscaped courtyard with lawns and looping paths. The townhouse enjoys its own private entrance, two wood-burning fireplaces and a finished basement (with a recreation room and its own laundry room outfitted with a full-sized washer and dryer).    Features include: an entry vestibule; center hall; living room (with marble-surround fireplace and eastern picture window); 22-by-11-ft. formal dining room; windowed eat-in kitchen (with granite countertops, 2 sinks and stainless-steel appliances); master bedroom suite.    Dogwood Close has an on-site super (since it's a co-op and not a house) plus a central laundry facility. And the complex is across the street from a private seasonal swimming pool that allows outside membership.    Monthly Maintenance $4,170.73, includes heat and hot water, taxes, gardening and groundskeeping.    Close to parks, schools, buses and transportation to Manhattan.