Here is an ultra-wide (UW) lens you may want on your APS-C sized camera: the chunky Sigma 10-20mm f3.5 EX DC HSM. It will work on any entry-level Nikon DSLRs. It's Php 30,000-plus price tag is half of what branded models sell for. The 10mm is like 15mm on full-frame SLRs and the view is sprawling. Wide open at f3.5 the far corners are soft, so I use f8 to improve the overall image quality. The photos below are interior shots of the Asian Institute of Management (AIM) in Makati city for their new brochure. It's good enough for hi-res commercial advertising work and available light shooting.
In the last photo (above) I shot this outdoor event at 10mm f3.5. Central sharpness is very good but forget about the extreme corners. But if you can afford the Nikkor equivalent, then go for it. In photoghraphy-as in life in general-you get what you pay for.