of course you can. some spells are old and time tested, but all spells originated by someone creating them. spells actually are stronger if the person casting creates the spell. you could also try finding a spell and altering it to meet your needs. [like a spell calls for clover but you use cinnamon because you feel a stronger connection to it]
just be sure to research the ingredients you use, so they don't clash and contradict your spells intent. keep in mind also spells cast on the waxing moon bring things to you while cast on the waning moon take them away. spells can also grow more powerful of you cast them so many nights in a row [like 3 days before the full moon you cast the same spell with the same items each night at the same time finishing on the full moon] just research spells similar to what you wish to accomplish to get an idea of what to do, then research the items you wish to use to make sure they all work in your favour. blessed be.
I'm new to this of course, could the one who answered my post please send me a private email or someone who wouldn't mind to send me one? I have a question I'd like to ask more in private about doing my own spell.. firstname.lastname@example.org