A gtx 970 should be okay but it’s best to get the 4gb version if you ever wanna play at high settings. 2gb is a bit okay, but fortnite can eat up half of the 2gb vram and can cause some stutters or slow downs. If you can’t offered neither of those maybe get the gtx 1050 2gb version or the 1050ti with 4gb vram, just make sure you have 8gigs of ram and a strong enough cpu to handle those graphics card.
Oh yeah also forgot to mention power supply make sure it’s decent as the gtx 970 requires a 500watt psu as it draws 145 Watts and a 8plus 6pin connectors,the gtx 1050 draws about 75 watts so you don’t need any pin connectors for it al the power is being drawn from the pcie slot.