I'm not sure if this is too late, but building a drop in is relatively easy. It consists of two (three including a ladder) main parts, the platform and the ramp down.
To make the platform, first decide how big of an area you want to stand on, I'd suggest 4 feet x 4 feet, but smaller will work too.
Once you have that determined, cut 2x4's into the correct lengths. keep in mind that the 2" side of a 2x4 is really 1.5 inches and the 4" side of a 2x4 is really 3.5 inches.
so anyways, after you build the two squares, youre going to want to decide which is the top and which is the bottom. it shoudlnt matter too much. Once you decide which is the top, put a "stud" (a supporting 2x4) every 16". be strict on that to make sure you dont fall through the top of your drop in. once those are on, slap some plywood on top and you have the part you stand on all done.
The next part is deciding how tall to make your drop in. if youre planning on using just a sheet of plywood as the ramp part, id suggest a 4' drop in so the pitch isnt overly steep and your transition isnt too rough. once thats settled, cut 2x4s to the proper height. To make your supports strong, i would suggest using 2 2x4s meeting perpendicularly at the corners to form an L shape. This is makes your supports much more strong than a single 2x4 and you wont need to spend the extra money on a heavy ass 4x4. once you have 4 of these Ls made, put one in each corner and connect the top and bottom pieces you have made.
Now you have the platform done and you basically just need a ramp. These are usually pretty easy to make and can be done a variety of ways. One method that I've used is constructing a ramp that just slides into place and isnt actually attached to the platform. To do this, measure the distance between two of your vertical supports. this should be the width of your platform minus about 10", depending on how you actually made it.
Take this distance and cut a handful of 2x4s to this size. These will end up being the studs on your ramp, so make sure you have one every 16" or so. Then, take two full 2x4's (8 foot lengths) and begin connecting them with the studs in between them. You're going to want to leave about 6"-1' of 2x4 sticking out for under the ramp though, you will use these to connect the ramp to the platform (I know this part is getting confusing, try to stick with me). once you have the ramps framework built, attach a piece of plywood, being sure to leave that extra 6"-1' of 2x4 sticking out of the top. now you have your ramp.
To attach this ramp to the platoform, all you need to do is screw down one well placed 2x4 into the front of the platform. What will happen is you will hold the drop in ramp horizontal to the ground and slide it into the slot you've just created. then, when the front of the ramp is lowered, the "prongs" (2x4's you let hang off 6"-1') will wedge into the top of the platform and it should fit snuggly into place. I know this last it was confusing, so feel free to ask me about it.
As far as drop-in surfaces go, I recommend using pvc pipe. its a little tricky at first, but just remember to lean forward and youre fine. The PVC will be the quickest way to get speed and if you start having fall sessions with it, the pvc cleans the bases of your skis as you drop in on it. this keeps things a lot cleaner and faster.
Good luck with all of this and hopefully I wasn't too late. Feel free to ask Questions
