I want to know the effect of frequency within temperature range from room temperature to let say 250 C on loss modulus, storage modulus and glass transition temperature.
The effect of frequency is similar to changing the temperature ramp rate change. The higher the frequency, the higher the transition temperature (same is true for other properties that will show higher values in terms of temperature). Thus, with higher frequency (or scan rate) the higher Tg would be observed.
You can check out my attached presentation for descriptions of some practical work I did several years ago (fiberglass reinforced plastic pipe).
Keep in mind that as frequency increases, more brittle behavior is observed (impact is a high frequency event) and at lower frequencies more viscous behavior is observed (creep and heat distortion are low frequency events). Also, if you heat the sample too quickly, it will not be in thermal equilibrium and the data will not accurately reflect the real-world behavior of the material you are testing.