The thing with building a bond ladder is, you have to have a chunk to invest without touching it for a while at least until your yield can be rolled into more bond/cd's. This money should not be accessed unless you have an emergency.
If you have $1000 to start, try a $500 3 year and a $500 1 year. After that 1 year, roll that yield from the 1 year into another 1-3 year bond.
The longer the term, the higher the yield. Eventually, that yeild will pay for another Bond, CD. Now you have 3 and the 3 year is close to maturity at a higher interest rate. That's the magic of them...You always have something maturing soon.
Good luck man! If you need any investing advice, lemme know. 401K, Roth, ETF...whatever