The sky is the limit, as long as it’s legal.
I’ve seen some really creative investment structures and have come up with some curious and interesting ones myself. If it’s legal and there’s nothing in the state or federal law that prohibits you from partnering with somebody or putting a business together, then dream up a deal and agree on paper.
Your agreement may say that the investor has to give you $100,000 or $10,000,000 and they get 3% of the company along with access to your office. They might also get to walk your dog on the weekends and have a seat at the board table. They get to have a quarterly investment call just to listen in and make sure they know what’s going on. Maybe that’s the deal they want. Or, maybe they just want to simply give you the cash, but they’re also responsible for connecting you to two other potential investors every 6 months. Maybe they want to have access to your computer servers, your information, your spreadsheets, your financials, and 24/7 access to you. If that’s the deal you agree to, then its fine.
Whatever you all agree on is fine. Just run it by an attorney, to make sure there’s nothing wrong with it legally, and make sure you can hold up your end. Where you’re going to run into legal problems is often when you have employees who are also becoming investors or partners. That’s a little bit sticky with employment law, so be careful there.
Bottom line is, its a good idea to get a CPA and an attorney to look over your contract to make sure it’s kosher. Often, you can just write the plan or the deal down on the back of a scrap paper in your office, take a little notebook out and just jot it down. Put the bullet points both of you can agree on. Hash out the details, send it to an attorney, and let them turn it into something 10 pages long (as they love to do!) and they’ll make sure that it’s got the right bells and whistles to keep both you and the investor in the right page.