I recently had Cox install Panoramic modem/wifi combo. Extremely disappointed in the range and performance for my Roku players. Some simply do not play at all. Modem/router is in the center of the house and it's not a huge house(single story 2200 living). I'm thinking about purchasing my own modem and running three separate routers in the attic above the areas where my TV's are located. Does anyone have any input if this would work or not????

Wifi routers are designed to send out a signal on the horizontal plain, they are not great at sending a signal on the vertical plain. This is why people with multiple floors often have a router on each floor. You would be best advised not to situate routers above or below the floor concerned, stick to putting them on the floor itself.

Check your wifi environment. Make sure you're not fighting for space. Remember the differences between 2.4GHz and 5GHz (2.4 penetrates, 5 bounces).

If it's thick stone walls giving you an issue or some such physical dampening, consider electricity mains networking to a transmitter nearer to your Roku units.

Placing them in the attic area would provide sufficient coverage for the floor area directly underneath them, particularly if there's no insulation between the two. But Andy is correct that they will perform even better on the same plane (same floor). For your space, I wouldn't think that three would be necessary. My home is 3600 sq ft on three floors, and I have two routers set up on the top and main floor. the main floor serves the lower level quite well. Make sure they all support dual band, and .11AC if your Rokus are new enough to have that support.
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One reminder: make sure the routers you buy have the ability to install as Access Points. You don't want them to act a firewalls between your network segments. That way they all get their IP addresses from the same DHCP server and are all able to see each other. If you install a router as configured out of the box, you could run into all sorts of network connection issues. 

I recommend a mesh wifi system if you want to keep it simple.. my Google WiFi system works great with all Rokus in my house.. I have the main unit in my living room, a seocnd unit on the first floor near the basement (for the basement Roku) and the third unit to cover the 2nd floor. There's a little bit of a "confused spot" in my bathroom, where I'm guessing the main and 2nd unit can't decide which one is to connect to my devices there, but other than that, signals are very strong everywhere else. Even my detached garage gets a decent signal.

Also a good suggestion, Jeff!

Thanks Jeff!
I'm not that knowledgeable on wifi in general and usually struggle somewhat if there's any problems. I'm looking at the Google and it seems like it might be a good fit for me. Seems like a simple set up with all the devices working together.
We're not gamers or heavy computer users at all. 90% of our internet if for TV's.

Begin by buying 1 router to replace theirs. If it doesn't cover the area, then buy another.
You didn't mention your bandwidth, so it it hard to say how much you should pay for a router.
ASUS brand has fairly simple setup for using their product as your main router, or as a repeater.
Before you make any decisions, download a wifi analyzer app to your cell phone. Make sure the wifi channel you are using isn't flooded by your neighbors.