Amtrak Guest Rewards - point agr roomette amtrak?

hello I buy a ticket chicago chicago san antonio 125 dollar coach class and let me know if I can with my amtrak guest reward points for a roomette.

No you cannot buy coach fare and upgrade to roomette with points.
How many points do you have?

10000

then Buy 5000 points for about the same $150.00 and you will have 15000 enough for a roomette chi to sat.

As Darben said, with 15,000 points you can book a one zone roomette award. The roomette award includes the rail fare, so after you book your award travel wtih AGR, please be sure to cancel your coach reservation and get your money refunded.