Is this for inside or outside? How high will it need to go? The basic formula is 1 foot of ramp length for each inch of height. This is the maximum slope for a hand propelled wheelchair according to the ADA. If you need to get up three feet of height, that would be 36 feet. It does not have to be a straight ramp. It can make a 90 degree turn half way up. Check out this link to see if it helps. Unfortunately, the easiest solution is the most expensive, which is to buy a prefabricated unit.
i have a really thick solid oak door was going to try to use we only have 2 steps
The door might still be too steep. Does the door have a flat surface? If not, you could cover it with a piece of plywood, but you would still have to build a frame so it would not slip off the stairs.