I'm looking to build my own home. I can't afford any where near PJ or kl so I'm looking to anywhere about 20-40 Mins away. Anyone knows where are good areas? About Rm20 to RM70 per sqft.

There's Rawang, Saujana Utama, Puncak Alam Area and beyond.
Alternatives are also bangi, semenyih etc (haven't explore those areas yet).

Any advice which area would best in terms of value in future, development etc.

I can say Puncak Alam..Nearby UiTM, Setia Alam and LRT extended to Setia Alam. But if you're working in KLCC area. That is quite far..

If working KLCC area, Bangi, Semenyih should be nice. New highway SUKE to MRR2 / DUKE.
Gombak area should be ok too!