That up there ^^^^ is directly from G, AFN members. Let's help him out the best we can, and get him to growing some premium buds!!
G - 450w of lighting should have you well covered. 90° might be a bit high, and you might see signs of heat stress. Remember, heat rises, so it might be hard to keep the heat down in your attic. Browning leaf tips sounds like there might be some nute burn occurring, but pics would help us determine that. A very important tool will be a soil pH tester. The CWP A8 is highly recommended. Also, you will want a liquid pH tester to make sure your nutrient solution's pH is falling in the right range. What nutrient line are you using? There are plenty of autoflower strains that go from seed to bud in 8 weeks.
Autoflowering seeds.com is a great place to look around.