It's not recommended to write your first patent, especially if you have no prior training. The patent law requires that the claims be written in certain format. Simple terms such as "comprising" vs "including", and "a" vs "the" have very different meanings. Without proper training, you could end up with claims that means something different from what you envisioned. Also, if the examiner doesn't like how you draft your application, s/he can ask you to amend the writing. Here again, format of amendment must conform to certain rules. Each amendment also requires a fee, and the cost would accumulate.
A patent attorney/agent can draft a patent application that conform to the required format. Also, since the attorney/agent is not the inventor, s/he can provide an independent insight to your patent, not be blinded by presumption, and prepare claims that can realistically stand against invalidity challenges.
That said, don't totally rely on patent attorney/agent. An incompetent one will draft claims so limited that is basically a detailed description of your product. The patent will get granted because it's so limiting, and the attorney will get paid, but you'll get no protection.
Your job therefore is not to write a patent, but to have a good understanding on what's really novel about your invention and make sure the person drafting your patent understands that. Your other job is to make sure your patent cannot easily be circumvented. Your attorney is not the inventor, and s/he has no business coming up with many different embodiment of the novelty. You are the inventor, and it's your job to think alternative embodiment to help support the broadest claims possible.