Here's a personal tip ...
Generally I take my chops and arrange them as you do and layer over a quick beat to create a rhythm and then I'll play over it on the keyboard to create pads, basses, chords etc. It requires some theory knowledge, but not much. I'll share how I work.
So, you've got your chops and your drum beat and they're on loop. Next you need to find the root key of the arrangement you have created. You could run it through some analyzer that tells you the key, but that's no fun and you learn nothing.
To find the root key start hen pecking on your keyboard. The root key will be the key on the keyboard that sounds most pleasing to the ear in the context of the rest of the song. You should be able to press the root key continuously and it wont sound out of place against the rest of the song.
It's best to load up a piano for this, something that cuts through and is audible. Make a note of the root key on paper. You can use tools to do this for you but that's no fun and you learn very little.
Once you have found the root key you can then apply some basic techniques to figure out the scale of the track. A scale is just a bunch of keys that work well together. In western music it's mostly the major and minor scales that are used. Unless you're sampling Jazz, but the same thing applies.
Take your root note you found and add 2 semitones. This basically means move up the keyboard 2 keys. So if you start on a C, and you move up 2 semitones, you end up on D. Does that key sound good? If so, make a note of it. If not, move down a semitone, so if you're on D, move down to C#. Does that sound good? If so, make a note of it, if not, move up 3 semitones. This will put you on D#. One of those 3 will fit, unless you're making some crazy free form stuff.
When you find a key that works, repeat. Move up a semitone, or 2 semitones. Keep testing for keys that sound good. Your ear will tell you what does and doesn't. Make a note of them on paper. When you've got your notes written out you should be able to determine the scale of the song.
You can count the distance between all the notes. They will usually either be minor, or major. The distance between the notes for major and minor are below (ignore my crude image)
Remember also that just because your sample might start on C, this doesn't mean the key of the entire track is C (c major, or c minor for example). It just means that there is a C key in the scale.
I could write a book on this and get real deep. I do run a blog so I might blog it.
Once you've found the scale you have all the keys you need to work with. Just play around. Things get deep when it comes to functional harmony, but one thing you can do is create a chord progression for your melody.
Let's say the melody you create over your arrangement is for examples sake: C, F, G ... you can use that to make a chord progression.
Take the C note, move up 4 semitones to E, place a note. From the E move up 3 semitones to the G. Now you have a C major chord. Do the same with F, and G. To get a C minor chord instead of moving up 4 semitones after the C, move up 3 instead. This same pattern is used for any key you press on the keyboard.
Let me know if you want an article. I'd probably have to break it down into a couple so readers grasp the basics but I don't mind writing one up.