I'm building a raised flower bed in the garden?

Why not it would be perfect if you had a horse too

The above answer is good. Fertilizing and enriching the soil is a good thing, but there is something as too much of a good thing. Assuming you are starting with some sort of soil (not just using sand, rocks or bits of concrete), you shouldn't mix in more then 1/4 the volume of soil enrichment (manure, dried sewage sludge...etc). If you are just adding compost (different from manure) you can do 100%, but generally more economical to do 1:4 or 1:2 mixes.

Adding too much manure can make the ground to hot from the decomposition of the manure to allow for proper germination of seeds and bacterial growth that's helpful to break down the manure.

No mix the manure with good soil. Then through the winter months use the garden as a dumping ground for your used vegtables, rototill it in the spring and you will have nice veggies the next year.

a good idea lay newspaper down first it helps reduce weeds then some good hay add also good topsoil and mix in manure at 40% to much manure you risk burning plants i would recomend using Seasol (seaweed an fish ) this will help your plants grow stronger improving there roots to help prevent damage from frost to heat, its the poo .