We can't really stop you from doing that. You can go ahead and give it a try. You'll see why that doesn't ever work out.
Here's a short list of reasons because this can easily be 100 reasons and nobody has time to read that.
You'll need to find a competent developer (how long will he work on it, how much time will you spend looking for the right person or team?)
Who will design, what software will be used, how will it run?
Hardware costs and limitations based on the skill of the developer you hire, which is directly correlated to their hourly rate
Who will keep improving the system? Who will do maintenance?
What if you can’t find him anymore?
Add up the costs just for those alone and you'll see why it can easily cost you a lot of time, stress and at least six figures (in Php)
If you compare the price alone, just look at how long a monthly subscription with SeriousMD will take get to that "investment" cost? Now you can see the difference.
It's why the doctors that tried that are using SeriousMD now and fully supporting us.