The Pcs are level 1 with NPc classes and they re about to participate in a festival in order to gain some money in the competitions the festival have.
I am planning to do an obstacle racing, in fact two of them. One about endurance and strength and the other about agility and speed. And if possible a version where they can participate individually and another where they have to make it with a group.
The method to deal with the obstacles is to use their skills, but the problem is that I do not want to just ask for rolls.
Roll acrobatics, then roll climb then roll acrobatics again...,nah.
A skill challenge is not fun if you have no choice but just roll.
So, how to design skill challenges without railroading everything? And what obstacles (and associated skills to solve it) can I use?
I would do it as a chase. The nice thing about Pathfinder chases is that there's a choice to be made at each stage.
The chase rules Blueluck linked are a good start. The great thing is that the template is very easy and basically writes itself. If you can do without skill checks I don't know, but I know from my own experience that if you describe the chase and keep up an approriate speed (no time for the group to weigh their options for half an hour!), it doesn't feel particularly railroady.
I created two sets of my own chase cards, woodland and urban. Unlike the examples in the original rules, I created a few cards that have two obstacles and three of four choices in that stage, just to mix it up a bit. It's ok to think outside the usual box of rules when designing chase stages, since you want to involve many different rolls. So a slippery roof could be overcome by either an Acrobatics check or a Will save (afraid of heights?), for example. Few characters will have high bonuses in both rolls and therefore you have an option for the casters and one for the agile types. The next stage might involve climbing down a scaffold, so maybe you offer a Climb check or a Perception check (maybe there's a shortcut?).
It's ok that the chase options tend break the 4th wall, because it allows you to maintain a high speed of play. A friend of mine fiddled with FATE aspects in chase scenes, and it might work for some groups. Basically you include a new layer of option in each chase stage, and say "If you grab one of those rusty pipes while running to the door the escapee just slammed shut in front of you, you'll get a +2 bonus to your next roll." Or something like that. The trick is to not allows this for free in every stage, because then everybody would do it every time. Limit it to three times per chase instead, or if you use Hero Points, include them into the chase.